Pricing:  Home Depot carries a couple of different sizes, with a 12'x15' size running about $16 and an 8'x12' size at $8.  To connect more than one together I just use clear packing tape on the back side.  The last two years my main backdrop has been 12’ x 30’ and last year I pieced four together for an 8’ x 48’ design.  I haven’t ever seen this dropcloth at Lowe’s but it was on the Home Depot website if you don’t have one nearby.  Hooks and paint are also inexpensive.

Painting:  For large areas of background color I recommend a garden sprayer (but not one that has been used for pesticides).  I just mix a little tempera poster paint in with the water to get a color I like.  The variations in the spray coverage make it look realistic.  Then I use all kinds of paints to paint in the detail work (poster, acrylic, sometimes latex).  And because the dropcloths are so lightweight and they have the moisture barrier, I have just pinned them up to my living room wall.  That would make it easy if you wanted to use an overhead projector for some of the detail, especially if you don't consider yourself "artsy."  I haven't had any problems with paint going through to my wall.  And a little paint will go a long way ... whereas canvas will soak up more paint, the moisture barrier on this dropcloth is great.

Hanging:  I use Command hooks attached to our gym wall, spaced every 5 feet (so a 12'x30' backdrop only needs 7 hooks).  I poke holes in my dropcloth for hanging, reinforce the hole with strips of packing tape on the back, and pop a shower hook through the hole.  Then you just have to slip the shower hook over the Command hook.  Once you're set up and you go back to actually hang your backdrop it literally takes just minutes.  If you are stretching across an open area where you won't be able to have hooks I would recommend making some sort of loop across the top in back and running a dowel or something similar through to brace it so it doesn't droop in the middle.  As for the hooks, they are removable, but I'd leave them up unless someone said something.  Mine have been up a few years and I'm in the room every week but never even notice them.  And if you're maybe thinking about painting something else that might be used in a room with a drop ceiling I've used binder clips from the back to hang in that type of area (but still reinforce with packing tape to make it stronger).