If you want two subs and a pair of components you're going to have to make a sacrifice. In order to use the Crescendo amp, you'll have to opt for a pair of subs that require little power (200 - 250 watts rms each). The other alternative is to buy a pair of amplifiers ( a monoblock as well as a 2 or 4 channel). You aren't working with a very big budget, so the overall quality of the amplifiers you can afford will take a dip if you have to buy two of them....unless you purchase used equipment.
Do you think you won't be satisfied with a single subwoofer? In all honesty, a single ID Q will perform well if you have an enclosure built to ID's specifications.