Welcome to the Quilting Board!
I used a large quilting hoop when basting to hold everything tight.
I use quilt frames. One set is at least 100 years old, a "double bed" size I stapled a denim strip on all my sticks to which I pin the quilt. (My mother-in-law used thumb tacks.) And I use bolts to hold the sticks together. (C-clamps work, too.) I have two sticks that are 96 inches long; made by my son from the old baseboards in this house. I have two more sticks 48 inches long for small quilts. I use them all, all the time. Everything is pulled really tight. I can pin-baste a quilt in about an hour. If I'm going to tie the quilt, that takes longer. Everything is smooth for FMQing.
Before I discovered putting the dogs outside - I used our bed. Now I put the dogs outside before putting the quilting all together with batting and back, vacuum the floor, and proceed. Once I'm finished, the dogs can come back inside.
I use the top of our pinging table! Love it for the large quilts.
I hear you on basting spray not being in the budget Keep an eye out if you have a JoAnn's or Hancocks, every once in a while I'm able to pick up a can for less than $5 using a coupon. And once in a blue moon it will show up at my Wal-mart for $4! These days I'm literally saving my pennies for quilting goods lol oh to have disposable income again lol someday
I have one of the craft tables similar to the one available at JoAnn's that the sides fold down. Use it for cutting, ironing, everything. As others in this thread have said, center the backing, clamp with the binder/bulldog clips from the office supply stores. I use 3 on each long side and 2 on each short end. Smooth, clamp. Lay out the batting, smooth, start in the middle of one of the long sides; unclamp first layer and then use same clamp in same position for the 2 layers. Repeat process with the top. I then usually pin baste but it it's a king will sometimes thread baste to keep the weight down. Then just reposition as necessary until the whole top is basted. Sometimes takes some time but I'm not on my hands/knees and I'm not bending at all kinds of odd angles. Back and knees just won't take that kind of abuse.
I can't get down on the floor to baste. I use my ironing board over which I have placed a 4 x 6' sheet of plywood. I clamp the backing tautly to the plywood, spread the batting smoothly, and then put the top on, and clamp it all around. No puckers or wrinkles and no hurt back or knees.
Ask if you can use the space in a church, library, school or other local building that has large tables. I do this and most are very accommodating and then I can tape my back down smoothly, continue layering and then I pin baste. My quilt guild actually meets for a work day at the local library and we can layer many quilts in the space they allow us to use. Some work on the floor, others on tables.