I get a lot of questions about framing & mounting options -- and there are so many choices. But here are several options you might consider when framing your artwork. See the example below that illustrates how I like to frame these prints.
$10 - $50On the less expensive side, you could get some minimalist frames like these: Format Frames or these: Imperial Frames
NEW FROM CRAIG FRAMES!!! $15 - $22Now you can get a wide variety of 13" x 19" frames the hold these National Park posters -- perfectly! They range in price from $22 for a single frame to $15-$20 each if you purchase a 2-pack or 4-pack. Some of the styles are real wood, too! You can see them here: Click here for Craig Frames BH Photo has a ton of inexpensive frames to choose from...and you can keep the price well under $50. Click here for B&H Photo Frames
$50 - $99
Next up would be a more DIY route. I would try to find a 18″ x 24″ frame at Michaels, Target, Hobby Lobby, etc., for framing a poster. Hopefully one that's on sale -- or even on clearance. Then, just have a custom matte board cut to fit the poster and the frame. I have the inside of the matte cut to 12-3/4" x 18-3/4", which is enough to hold the print down, but still display the number, signature and date. You could add a second matte for a more substantial look, and I would have that cut at 12-1/4" x 18-1/4". With one or two mattes, you can choose the color(s) to match the print, the frame, and or your decor. I've found Hobby Lobby to be the least expensive place to have matte boards cut.
Then you just need a little double-sided tape, a ruler and a little patience to mount the poster to the backer board, over lay the matte board(s). Then, slip it back in the frame and tighten down the tabs in the back to hold it all together. You might also want to buy a wire hanging kit at the craft or hardware store. Usually with two screws, you can attach the wire so it's ready to hang! Depending on your frame choice and number of matte boards, it's possible to go this route for $50 - $99.