How much should I expect to pay to recoat my bathtub?
Are there any do it yourself products to recommend, or should I stay with a professional?

The DIY product that the people before me used went to crap in a year and a half... but I planned all along to redo the bath so it's a minor thing. I've heard decent things about the professionally done stuff here.

Can't tell you what the people here used. I know they scuffed the tub before applying (like you're supposed to), but the product just didn't last .

Here is a previous post about this that might help...

https://www.askmehelpdesk.com/interior-home-improvement/painting-bathtub-69669.html?highlight=tub+refinish

I think the last quote I had was around 500 to 600 for a tub, in gloss white. Its been a few years since

I would not do a recoat unless I was doing a quick flip of a condo or home. Recoats do not last long enough to pay for themselves. There are companies that install a fiberglas shell liner for about $350 but I have not done one.