For instance: My own total black backdrop is just a piece of lighteating poly velvet I bought from a Remnants bin at Joann fabric for like $6. You can get pretty nice scenic pictures printed on cloth and labeled as "Tapestries" from Society6 or Amazon for a lot less than the vinyl photo backdrops out there. Pin or tape those up on a wall, try to match the lighting, and ta-da, nifty photos. Mind you, have I a few really nice vinyls from Etsy producers because they had some very good ones on occasional sale. I also often shoot my tinies in front of pieces of Scrapbook cardstock, which comes in every imaginable print and texture and color.
I use framed canvas as it's rigid. It can be painted, have fabric stapled to it, as well as just left plain. I have in different sizes and some are plain, while others have special stuff on them.
I have a massive roll of plain white paper from Amazon. It's easy to draw on, embellish, poke led lights through, etc, and is a quick foundation for more elaborate scenes. I also have a few fancy backdrops from eBay meant for 1/3 scale dolls.
I prefer to go outside for photos - lots of easy and free backdrops, but since that's not always possible, I've used all kinds of things for indoor photos. Current favourites are leftover floor tiles - they're too small for SD but work great for MSD and tinies - and a variety of fabrics. Another suggestion for a variety of backgrounds is a computer screen. You have to play with the lighting to get it to not look weird, but can work pretty well: this photo was taken that way. Generally best to use your own photos or ones with proper licensing, but there are endless possibilities.
For both solid color backgrounds and a cheap reflector that's easy to lean against things and position on its own, I always recommend foam board. They come in all sizes, and they don't need to be pinned to another structure to stand. In fact, sometimes I get lazy and pin my fancier photo backdrops to it instead of using my actual backdrop holder. I also sometimes pick up sheets of washi paper at the local art store that look interesting, and they can make for nice head shots for my guys. (I have pretty big dolls, so they're not big enough for a full backdrop.) I've also used wrapping paper with interesting designs, and contact paper over foam board depending on what sort of pattern I want. (There really is no beating just taking a doll outside and letting nature paint pictures in the bokeh behind a doll though.)
Before PhotoBucket went to the dark side, they'd have really good sales on canvas prints - and I got 4 of my own photos done as very large ones (SD size as in 3x4 ft!!) for extremely cheap. Maybe $10 each? on very good quality canvas
If you have a DSLR and like bokeh, crumple up and then lightly flatten some tin foil. It'll change your life. XD
I've used curtains, gift wraps, fluffy blankets and as Tayma-Leigh suggested monitor backgrounds like in this picture: Small Scale Marvels : Photo
For pure black I use the velvet side of our table pad. I'm really fond of mat board both to use as a backdrop alone or to support other backgrounds. it comes in 32"x40" sheets. I get it cut in half. Use one half plain and airbrush some detail onto the other half. I use 20"x30" poster prints of my photos. I use art paper. I use scrapbook paper I make 12"x12" prints to use as portrait backgrounds. I select my dolls out from the background and composite them into fantasy scenes.
I don't have a BJD, but with other dolls I've utilized the wrapping paper as wallpaper idea: I use cardboard display boards as walls and cover them in wrapping paper, and then I switch the walls out in my doll rooms as needed. I would think that that could work for BJDs, too.
I've used a lot of things for backgrounds- bookshelves, walls, curtains, a sewing machine cover... but I think that my favorite background for pictures (though it isn't plain) is probably my window. I like the dramatic lighting it creates too.
I am new to the whole BJD photography (but not photography in general). I went to the dollar store and picked up a few sheets of the glittery cardstock. When light is applied to the front, the reflection creates some pretty beautiful photos!
my one 'window blind' (a custom one to start with lol) has been a back drop for my SD's quite a bit at the begining. It goes down to the table they can stand on and i put a small matt rug on the table... my curtains i let fall dapey like. this is my iple 65cm girl Luna... but in this you can see it's essentially the blind down drapes pooled and on my nightstand... the 'rug' is normally for the cats to be comfy so yes it lives there too lol I did see another 'monitor' type one where someone used their giant TV screen with a picture on it (like fed thru a camera of some kind) for a half body shot of a big doll like this