Hi jedinat,
Do you have access to power tools and are you handy with such? If so, you can build a really solid platform bed for around $100.00, and that would probably be the best way to maximize your budget and have something that would be very solid and quiet.
There is a how-to from one of the site members here, and quite a few other links to DIY options in the slatted bed section of post #1 here.
Just something else to consider.
Phoenix