Most tub enclosures, like the one pictured, use a 1/12 to 2" nailing flange down each side and along the top. They are also designed to be used with tubs that have an anti siphon lip along the wall parameter of the tub. It sure looks like you have very little extra relief between edge of tub/tile to the actual corner. In order for the surround to fit snugly to the wall, it must be secured using this nailing flange. I think that you may have to build out the edge of that corner, thus reducing the opening size of the pocket door by an inch or two. This would not be very difficult, but would require some extra finishing work and some changes to door trim etc. If this clearance issue is the same on the opposite side of the tub, the same procedure may be necessary. Also, if you find that your tub does not have the anti siphon lip, extra attention will be needed to seal this joint. If and when you get to the point of tearing out the tile wall, be sure to insulate the stud wall and cover it with a good 4 to 6 mil vapor barrier, tuck tape any joints and the sides and top. This will provide not only water protection, but give you some degree of sound deadening to adjacent rooms. Use only MR (moisture resistant) or paperless drywall to finish off around your new surround.
A completely different approach might be to cover the existing tile with a glue on surround kit. Assuming the tile is secure, after carefully cleaning all soap residues and prepping the surface with a dewaxing agent, (isopropyl alcohol for example) trowel on adhesive and install the kit. There are actually some nice surface mount enclosures out there, usually five piece. the box stores typically only have one or two choices and are pretty cheap looking. Check out a specialty kitchen and bath supplier for a much better selection.
The most common discrepancies in price between tubs, not counting accessories like heaters and jets, are due to four factors: style, depth, build quality and brand. A garden tub will generally cost you more than a simple rectangular built in, and a clawfoot is more expensive still, followed by "custom" installations like non-overflow tubs.
In the same style, the depth of the tub determines the volume and weight of water the tub must hold and therefore the dimensions and thickness of the material. More material == higher cost.
Even in the same style and depth, one maker may build their tub out of cast iron while another uses plastic, or even in the same material, one maker may double the thickness of the tub walls to increase durability and thus longevity (removing a damaged built-in bathtub is no small job; it can even require a full remodel because it requires re-tiling the backsplash).
Lastly, major name brands will command a higher price even if their product is inferior. Jacuzzi, for one, is a trademarked brand name that has apparently rested on its laurels; I was warned away from even their thousand-dollar tubs for quality reasons, but the tubs still cost a grand, cause they're branded with a universally-known name (so much so that people use the brand without knowing it's a brand, similar to "Band-Aid")
As far as actually what to look for, it depends on what you want. For an upstairs bathroom normally used by kids and guests, a standard Kohler, Moen or American Standard acrylic or cast built-in is fine. Cast iron is more durable, and holds the heat of the water well, but it'll be a beast and a half to put in place. For your own master bathroom, you can be pickier. The three brands I mentioned are names I trust, and they make tubs in all shapes, sizes, styles and pricepoints.
Best Answer
Take it back as defective if it's not to stated specs. Trying to wedge the bottom flush until the floor goes in could crack the finish, if it's just bent out & not actually braced out. If the back wall isn't load bearing, you can plane or cut those studs back, plumbing re-alignment shouldn't be a big deal. Or, add another drywall layer to the foreground wall & make up the remainder with the tile layer. Or. just add tile edging with an ogee type edge.