Cleaning up the worst of the blisters should be 6-15 hrs max (unless you have thousands of them, which we can't judge from our screen....). You'll then need to sand, then barrier coat (interprotect 2000), witness coat and final bottom paint coat. So about 10-12 hrs of painting and prep.
So let's say 25 hours to be safe x $135 per hr is $3375. You then have another $1000 of paint and fairing compounds, plus another $200-$400 ish of supplies (rollers, tivek, goggles, tarps, etc...).
Now at most yards, sanding and painting is unskilled labour, should be around $75 ish per hour.
So $4800 ish at the top end, for labour and supplies (not including yard fees). For reference, in a cheaper yard (Texada), I was quoted $2500-$3500 for a similar job on a 28' sailboat.
I'm sure that for $20 000 it would look like new .... but that is probably not what you are going for? Talk to your contractor and explain that you just want it sealed, but you aren't looking for the perfect racing hull. Did you ask them to fair the bottom? That would be a really big job. I would just fix the worst / larger blisters and move on...
If you were to float it, sail across the straight and haul out 2 days later in Vancouver, your boat would be none the worst for wear.
Unfortunately, there is no relationship between the cost of repairs and the cost of the boat. In truthness (is that a word??), a really cheap boat can be a really expensive boat if it needs mechanical, hull and rigging repair.... Hopefully all these repairs were reflected in your survey and the price reflected the condition oof the boat. Now here's where it gets funny..... Let's say you bought it for $35 000, then spend $20 000. You probably still have a $35 000 to $40 000 boat.... replacing the mast on a 3 yeaar old 35 footer and a 20 year old 35 footer costs the same!
Keeping things in running order doesn't add that much to the value of the boat, but it allows us to keep enjoying and using our pride and joy. We just look at our annual maintenance bills as the cost of our vacations!