Sorry Frank, but tight budgets and good ways to fill/cover pools might be mutually exclusive
How long are you planning on living in the house? If you don't plan to ever move, then fill it with rocks, concrete, boulders, dirt, sand, -- what ever you can find. Since you have budget concerns, you might want to haul all this stuff yourself. Fill dirt can usually be had for free, but you'll need to search the newspaper or craigslist.com for ads.
If you plan to move during the next few years, or don't want to haul several tons of rock/dirt around, it might be better to drain the pool and cover it somehow. How about buiding a deck over it? I don't know how wide your pool is, it shouldn't be too hard to do. This way, when/if you sell the house, the new owner could use the deck as is, or move it and fill the pool.
Long steel I-beams would easily hold the load across the span of your pool.
not necessarily a DIY job though.
Just a thought.