Cheapest way out
I think the cheapest way out of this blister problem is to grind off the blisters and wait for a couple months as Jeff said. Then mix some epoxy with colloidal silica until it has the consistency of jelly, apply it with a flexible 4 inch wide plastic applicator, then roll on one two more coats of epoxy.
Those blisters look just like the ones I fought with this spring. I had my boat sand washed but I could have used a grinder. I used MAS epoxy because I got it cheaper at Boaters World. MAS epoxies has a help line (and the co-owners take call on weekends from their cell phones).
I coated almost the entire hull below the waterline with the coloidal silica/epoxy mixture. That's how many blisters I had. The MAS people told me that the first coat of epoxy seals the hull; the next few coats help protect from deep scratches. I applied a total of four coats but you could probably get by with two; that would save money. Epoxy is expensive.
Like Camaraderie said, you don't want to sinik a lot of money into a boat that probably will never be worth much if you wanted to trade up to a larger or newer boat.