Plastic/Glass for a very large, custom frame I am working on a large poster to display my original Pokemon cards, but because of the size of the cards and the way I wanted them to be laid out, store bought frames are out of the question.  The poster is not 100% done so I am not sure what the final measurements will be once I trim down the poster board, but it probably will be 49 inches by 29 inches. All of the cards are in sleeves, but I still want something over all of it to keep the cards flat against the poster.  What kind of plastic or vinyl or glass (though I don't know how I'd cut it) would be cost effective (at most $25), easy enough to cut to size, and not a pain to apply (like with phone screen protectors, it is hard to get the bubbles out).  Thanks!
A clear Mylar sheet could work.

Clear, moisture resistant, acid free and archival.
And available in the size and price range you are looking for.

Here's an example available on Amazon 
https://www.amazon.com/gp/aw/d/B0027A3HKG/ref=mp_s_a_1_1?ie=UTF8&amp;qid=1473127673&amp;sr=8-1&amp;pi=SY200_QL40&amp;keywords=clear+mylar+roll&amp;dpPl=1&amp;dpID=31N50Emps-L&amp;ref=plSrch