When buying a mirror, smaller is cheaper – I bought four 30x30cm mirrors for $9.99 at IKEA (online here), and staggered them. Then, I used them as a backing/frame for photos I had printed at WalMart and London Drugs for really decent prices (If I bought a frame for each, it would have probably totalled around $50-$150, depending on the frame). If you’re doing a photo collage, buy as few frames as possible, or take an hour to mat them yourself!
Also, use what you know: I’m decent with photography and photoshop, so instead of spending a bunch of cash on these photos, I took them on our mountain, photoshopped them, and printed them out. Buying prints can cost anywhere from $5-$50 per print, in general, and there are ten here!

Lastly, take advantage of your budding artist friends. You can sort-of see in this photo are two sketches/paintings at the end. the little one is a brilliant artist, and I hooked her into giving me one of her old sketches (which she was going to throw out) a few years ago. For Christmas that year, she painted them, and I bought frames and put them up. (Frames: $10/each, with a 40% off one item coupon from Michael’s. I bought one the first week and one the second, saving $8 – almost enough for the mirrors, lol!)