Blasted a few vintage/ muscle cars over the yrs.

Vapour blasting is a lot quicker than soda and the blast medium is heaps cheaper than soda

Had exactly the same problem and had my boat vapour blasted last year and then copper coated. I really rate Coppercoat.

MEC Marine did the work for me and was not that much more expensive than traditional antifoul if you are up for a scrapeback anyway but expect a 10yr lifespan rather than 2 yearly recoats.

The blasting is the most critical part. No matter what medium they use a poor operator can easily blast through the gelcoat and into the fiberglass so my advice is to watch them really closely.

The other consideration is the haulout/hard standing cost. I used The Landing at Orakei - saved over $1K compared to the next cheapest local marina.