Well, you've found something I've never been able to find. However, the mouldings are the most butt ugly I think I've ever seen and the shipping on a frame that large would be quite high. A 50 x 34 would frame out with a three inch matt to about 56 x 40, which when crated for shipping would be larger than UPS will take. Shipping alone could easily be $150.00. The width of the mouldings shown would be quite flimsy in that size which would mean a lot of wire reinforcing behind the print to handle the print, matting and backing. Glass for that size, again, would be very unwise.
Is this a "fine art print?" In other words, is it on archival paper and requires museum mount custom framing?
I'll wager to guess by the time you ordered the material including the plex (they plex prices are quite high), you'd likely save very little. Plus the problem of a user trying the fitting operation of the piece complete with a dust cover (I always recommend black kraft paper backing because bugs don't like it).
Why not give it a spin and see what it comes up to? I selected their "RP345" 1 1/2" wood frame with acid free foam backing and plexiglass (they won't do matting on frames larger than 84" united which his 50" x 34" piece would be) and it comes to $118.44 + $21.21 for UPS Shipping. That totals $139.65 delivered.
I don't represent these as being the world's finest frames - they aren't. They are however, as good as what you'll find in your run of the mill frame shop. If someone thinks they want better quality then by all means, go to a custom framer and pay for it.
I had a litho framed/matted a few years back in a custom framing shop and it ran me slightly over $275. I bought 2 frames with matting from this place last month that, as it turns out, are the identical materials and I paid under $120 for both of them together. I just had to do the mounting and backing myself.