Get out your sander and DIY. Unless you have a kitchen full of Corian to go with it, refinishing a vanity is too small of a job to interest anyone. The job minimum is more than you would want to pay.

I'll pay someone to do it. Don't trust myself.

Watch a couple youtube videos please. This is perfect entry-level DIY. Nearly impossible to screw up.

understand that some would do this themselves but thats not us so asking for help finding pro

You do not even need power tools to do a sink. You can just sand it by hand, with sandpaper. This is very simple.

If you're insistent upon getting a pro, the pro is going to worry that he can't charge enough. Disabuse him of this notion please.

If you are ready to drop 1K on getting in a pro, you might as well replace the whole thing as refinish it. Same costs. If you can scrub a pot or pan, you can scrub the corian with sandpaper. You have nothing to lose by trying. Start off with about a 100 grit if you have deep scratches, and work your way up the grits.

I a friend in the Bay Area fell in love with my corian kitchen counters and now wants them in their home. They are having a really, really hard time finding anyone that carries and installs them and the one quote they got was astronomical. This is not a very widely used material anymore and it seems especially not in the Bay Area.

I 100% get wanting to pay someone else to do the work, even if it is a high cost. If you can't find somoene to do it, budget how much it would cost to get a new counter, then launch into your corian DIY youtube project knowing that if you totally F it up, you'll be spending X bucks on a new one.

You might try calling West Bay Plastics https://westbayplastics.com/ 

They are a fabricator, but may be able to suggest installers in your area.

Good luck.

Replace the entire top, get an under mount porcelain BOWL.

I dislike integrated Corian bowls. Not quite enough gloss, hair and toothpaste remains like glue after years : )

Otherwise? SAND it yourself, because it is an easy task. I do my own kitchen tops. You can't do this??

Scrub the sink with Comet Cleanser........

Sand Out Minor Scratches

Inspect the sink for scratches that were not removed by the scrubbing. Sand remaining fine scratches with 400-grit sandpaper, either sanding by hand or with a small power sander. ( you can rent one at an Ace Hardware, probably )

Buff and Rinse the Sink

Buff the sanded areas with the scrub sponge or scouring pad to blend them with the surrounding surface. Rinse the sink thoroughly. If all this takes an hour of your time, I will faint.

From Amazon ~ $20: Micro-Mesh Corian Countertop Repair Kit

IMO a 20 yr.old sink owes you nothing and time for a bit of an upgrade or DIY and see how it looks and then decide.