Speaker repair...is it easy?

I've done many speakers from 4" to 12".
There are kits available from Just Speakers or Orange County Speaker Works online, just to name a couple.
Its very important to keep the cone centered around the voice coil, or it will rub if  the surround is glued crooked. Some kits include different thickness shims, in order to keep things centered.  That requires cutting away the dust cap, centering the cone with shims, gluing the new surround, and replacing and gluing the ,(usually provided), new dustcap that came with the kit. Use isopropyl  alcohol and q-tips to clean the old glue from the frame.
Just Speakers,(not affiliated with them), provides full instructions.

I never try to do this, because of the voice coil gap tolerance. I leave it to the pros. 

Gabriel Sound in NJ does my Altec 604Cs. Price is reasonable.

I agree with the others, that having them done by a professional is the way to go. Like many have mentioned, you can find someone who’ll do a perfect job, at very reasonable prices. The person I use worked for a speaker manufacture, and when they where sold off he retired. With the amount of work he’s doing now, his status has changed to semi-retired. Cost for replacing a surround is usually around $50.

What hasn’t been mentioned yet is the testing of the speaker once it's been repaired. I’m sure most of the pro’s include this as part of the job - I know the person I use does.