As a homeowner who has done his own bathroom remodels three times (three different properties; not all in one house!), I say do 90% of the work yourself. Get in a pro to do the plumbing rough-out and the finished tile. Do all the rest yourself. It doesn't take any more than a hammer and some patience. But don't do any of that work until you buy the house. A new bathroom increases the price $10k. A bathroom that needs to be re-done decreases the price by $25k. (Numbers I completely made up on the spot, but "feel" kinda right.) And it is WAY EASY to get money to work on the house you own. EVERYONE wants to give you money for home improvement.
Lovely. So the meat and potatoes for my practical points would be 1. DIY most everything but plumbing and final tile finish 2. Use the bathroom in need of remodel to negotiate on sale price 3. Don't begin work on said bathroom until the sale is done. 4. Homeowners have access to better lines of credit for this sort of work anyway.