Ah, I see. I have a HackRF and several USRPs, so I'm kinda spoiled in terms of bandwidth and capabilities. You could try combining more than one RTLSDRs into one virtual stream using GNURadio. Check this out: http://www.rtl-sdr.com/combining-the-bandwidth-of-multiple-r...
The only catch is that it is not phase coherent, but if you're doing FSK or AM then that's perfectly fine.
What? RTLSDRs go from ~$9-$20 max (I got mine for $10 on eBay), and a Raspberry pi is $35. The PandwaRF is ~$150 USD alone. Does the CC11xx series chip in this device make a difference to your use case?