If those posters say something about Capital Studios on the bottom, those are real promo subway posters. $300 really isn't that much, I went to a local "discount" place here in SF and they wanted $600 each.
I ended up having mine done in Los Angeles. I used acid-free backing, which won't discolor the posters after a long time like most other backings will. Real Plexiglas is better than glass. If the frame falls from the wall or is dropped while moving, the glass could break, cutting the poster. Plexiglas is a word often used synonymously with acrylic sheeting, like how Kleenex is with facial tissue, but real Plexiglas is the best acrylic sheeting. The type I used is UV resistant, meaning the posters won't fade when exposed to direct sunlight.
Metal framing is better than wood, as wood has natural acids in it which could stain the borders of the poster.
I consider the posters to be works of art, which should be preserved for antiquity. If you think of it in those terms, $300 each isn't all that much. Just be sure they use quality materials. So many people have generic crap on their walls, like Ansel Adams photographs or those lame reproductions of '30s French advertisements. If you plan on loving The Smiths for the rest of your life, I would say it's worth the expense. It's only money, I'm sure you'll make more. If you can't afford to now, then roll them up in a nice sturdy tube for sake keeping until you can. Do it once, do it right. It's cheaper that way.
And you were correct in posting this in the COLLECTORS FORUM, as it's a question about a collectible, not something you are looking to sell or buy. Overzealous moderator alert.
