They make shower pans that specifically replace standard bathtubs with the drain in the same location. Kohler, Americh, Swanstone, and Sterling, (as well as others) make them in various materials from Cast Iron to solid surface to acrylic.

Code has changed for the size of a drain serving a shower. You need 2" now. Talk with your local inspector to see if you can "retrofit" and be acceptable. I would think as long as you aren't putting in a half dozen body sprays and 2 rainshowers that most inspectors would be OK with it. But, better to find out on the front end. Nothing worse than to be in the middle of a sales negotiation where a buyer checks out the permits on a house and doesn't find one. That's leverage you don't want to give to a buyer, and would probably be worth a heck of a lot more than the $1500 quoted to do it to current code.

That sounds like a lot for 20 minutes of jackhammering up a trench and replacing the plumbing from 1.5 to 2"..... You could rent one and do it yourself a lot cheaper, IMHO. This isn't brain surgery. Plumb it, put in a "P" trap and re-attach it to the old plumbing.

Being "centered" is preferable in a shower and, you can mix up some deck mud and slope it yourself.

If you're nervous, go over to John Bridge dot com and start your own thread. We'll "walk" you through it....

Sue, my husband and I gutted and renovated our basement BR, oh about 5 years ago now. DH rented a jackhammer and redid the drain/plumbing himself. He was glad that he did, as the original owners had the plumbing so convoluted (you can see it partially buried in the pic). He also added a drain in our furnace room, (Figured he may as well while he had the jackhammer).

I would also suggest having storage space would be more appealing than elbow room to a prospective buyer, and certainly to a renter. Perhaps you can post a layout, and we can comment/make suggestions. We put a 4 ft vanity with drawers, and I LOVE all the storage space compared to the old 3 ft one with just two doors under the sink!