I know it's expensive so building a sharpening jig is the way to go.
Building a sharpening jig will save you time and money, as getting it sharpened by a professional can cost as much as the router bit.
The deep sharpening will also give you a clean blade and a crisp cut.
Here is what you will need to make router bit sharpening jig:
You will need pieces of plywood ⅝ or 3/4 “ thick. A band saw,a table saw or skill saw, a hand drill, drill bits, and a router.
A threaded insert, screws, A locking screw, wood glue, a file, 1 U shaped aluminum bracket with HPL inserts, 2 8” drawer slides, any heavy duty wood glue or PL, 2 bolts and washers,.two hose clamps, a diamond sharpening blade and an angle grinder.
First cut the main piece of plywood for the jig, about 1’ x 2 ½’.
Next, using the band saw, make two saddles for the angle grinder from plywood. These are to cradle the angle grinder. File the saddles down with a file to make them smooth.
Place the angle grinder with the blade in the middle of the plywood, mark where to put the saddles. Cut with a skill saw or table saw grooves into the bottom of saddles.
These are to fit the hose clamps. Glue saddles in place and screw one screw into the middle of each one. Put the hose clamps through the holes you made in the bottom of saddles. Place the angle grinder on saddles and fasten firmly with the hose clamps. Now, you can make the sliding glide table. The sliding glide table will sit in front of the angle saw. It will hold your router bit in place but it will slide back and forth so you can sharpen your bit with precision. Cut a piece of plywood 6”x 8”. Notch out a piece 1” deep x 4” wide, on the 6” side of the plywood. Then cut 2 pieces of plywood 1”x 8” each. Glue the two 1” pieces along the 8” side of the sliding table. This is the bottom. Now screw both drawer glides to the bottom of the sliding glide table. Cut a piece of wood 2”x 2” This will serve as part of the depth stop. Place the 2”x 2” piece of plywood at the back right end of the sliding guide table. About 1/2 “ from the end. Hold the 2”x 2” piece in place. Predrill holes for two screws and then screw into place. Now find the exact place to put the sliding glide table.Cut a new piece of plywood, 3”x 9”. Drill a hole ½” from the end. Using your router, make a slot down the middle, stopping ½” from the end. This is the main piece of the depth stop. You will need to have a locking screw to hold the depth stop in place. Holding the depth stop, drill a hole in the middle of the depth stop into the main jig. Now, screw the locking screw into place to make the depth stop exactly where you want it.
You are now going to make the top piece of the jig. Cut two pieces of plywood. The first one 5”x 7”.Measure ½” on both ends. Drill a hole. Use your router to make two slots on each end, making the slots 2” long. This is so once you have your bolts and washers in place you can slide the jig side to side. On the piece of plywood that is 4”x 4”, drill a hole on the end leaving 1”. Using your router make a slot that is straight across, leaving another 1” on the other side. The 5”x 7” plywood will be horizontal and the 4”x 4” plywood will be vertical. Pre drill two holes at the bottom of the 4”x 4” plywood. Having the slot go up and down. Glue the 4”x 4” plywood vertical to the 5”x 7” horizontal plywood. Drill the screws in. This piece of the jig will hold the attachment for the router bit.
Drill two holes in the middle of the sliding guide table.This is where you will attach the top piece you just made. Place the top piece onto the sliding guide table. Use the two bolts and a washer to fasten in the top piece of the jig. This should allow the piece to move from side to side, left to right. Now we are going to make the attachment that holds the router bit in place. Start by cutting two pieces of plywood 2”x 6”, This piece will sit vertically in front of the other vertical piece on the top of the jig. Here you get to the tricky part. Cut a piece of plywood 2”x 4”. Using your band saw, cut the 2” end, on both sides, down to 1” leaving enough of the back to fasten it to the bottom of the 2”x 6”’ piece. Now, continue with your band saw and cut a line into the 1” piece at the 1/2“ mark. Drill a ¼” hole near the end of your line. This is where the ¼” bit will sit. To sharpen your 1/2” router bit, make another jig attachment and drill a hole ½ ”. Glue the 2” part of the 1”x 4” router bit holder horizontally to the 2”x 6” vertical piece of plywood. Drill holes in the two 2”x 6” vertical pieces and add a threaded insert. Attach the two vertical pieces. Now we will add a locking screw to the side of the 1” piece to hold the router bit in place. Drill a hole in the side of the 1” piece of the attachment and add a screw. Take the sliding guide table and use your table saw or skill saw to make a groove in the top, above your bolts, to fit the U shaped aluminum bracket. Also, take the top piece of the jig and make a groove for the HPL slider. Use a heavy duty glue or PL to fasten into the grooves. Lastly, Put a 2” bracket on the left side of the sliding guide table. This is a depth stop to prevent the top of the jig from sliding off the bottom. Congratulations. You have successfully built a router bit sharpening jig. You can now sharpen your router bits like a professional. The jig should now hold your router bits safely, move up and down, side to side and have all other safety measures in place. When you test out sharpening your router bit, be sure to wear safety glasses and a good dust mask. Also when sharpening, be sure to approach straight onto the diamond blade from the side. Do this slowly. Once the router bit is sharpened, remove it from the jig and return to the diamond honing file. Wet the file and pass over 4-5 strokes. Wipe off with a clean rag. Your router bit is now just like new and ready for your next awesome project. Give your router bit a quick re-test to see the improvement.