When my husband and I bought our first house, we suddenly had 4 more rooms to fill with furniture. We needed a guest room (we have out of town family) but we did not have enough money to invest in another bed.
I sought out deals and bought a double high queen air mattress for about $40 and placed an old futon mattress on top (to add height and comfort). The bed does not have a bed frame but the window acts as a natural headboard.
I have left this bed up for 6 years with no problems. The pump on the bed has a convenient button that allows you to pump it up when needed. It is comfortable, durable, and has the look of a regular bed.