Tried the painting route a few years ago. Big mistake. Was not cheap, and started flaking after the first season. It was only a temporary fix, plus it added more cost to the plaster job.

Had the pool replastered two years later for $2500. Best money I've spent yet on the pool, made a huge difference in keeping the water clear and the enjoyment of the pool. Bad plaster makes for a bad pool.

Have you gotten bids for the plaster? You might be suprised. Also, get multiple bids. We got bids from $2000 up to $5000.