I'd give the benefit of doubt to a $50 subwoofer. I heard Infinity Reference subs are ok, just not the loudest on the block. Having said that, I use an Infinity Kappa subwoofer myself. However, I wouldn't cheapen out on the amplifiers. Anything cheaper than $150 (new) has a tendency to be junk. For the amplifier, I'd suggest PPI Phantom P600.2. You get solid 600watt RMS at 4ohms for like $160-170 in a ridiculously small form factor. 10 years ago people would kill for this. Don't get too obsessed about subwoofer selection. It's more important to get the box right. For vented, the box has to be made to match the parameters of the subwoofer, so forget about buying prefab vented boxes. Prefab sealed boxes should be ok though, as the only thing that you need to get right is the box volume. (and dimensions, to fit in your vehicle).