The QSC pieces are quite reasonable when purchased used (and there are plenty of them out there on everybody's favorite auction site). I have 5 DSP-4's that have averaged about $150/per -- they were purchased years ago though -- your DSP-30 is a better standalone option than the DSP-3/4's as the latter are meant to plug into the Dataports on specific QSC amps, but they can be used with a power supply and connected to other brands of amps as well. The biggest limitation is they are only 2 in/2 out; whereas you can buy an 8 in/8 out MiniDsp for $399 plus whatever shipping is to the US (does anybody know what the average shipping rate is?). The QSC Basis and DSP322 8 in/8 out products are big, big bucks though, selling for around $4-4300 new. I managed to jump on a used 922DZ a few years ago that a sound company forgot to list with the correct amount of digits in the asking price...it was a Buy It Now and I clicked the button and paid, they shipped it and I never heard any complaints from them...turns out is is CobraNet specific though and I don't know for sure yet if I will be able to patch it into my system without too many additional pieces. Going to have to enlist somebody with a much bigger brain than I to figure out the answer.
I've been very tempted by the MiniDsp products, but keep hearing many industry and HT install guys say they just don't have the quality circuits/parts to handle anything above the subwoofer range without jacking up the sound.