The littlebox preamp from Naiant.com (made by member mshilarious on ts.com) is $209, and is an excellent preamp, esp for the money. Do some searches on it to get more info, including comps of it vs a Lunatec V3 and EAA PSP2. If you want to go with an external preamp, I'd highly recommend it, particularly since it is one of the few options you have at your budget.
Jon/mshilarious is also developing a smaller preamp called the tinybox with a little more limited connector possibilities, gain, metering, etc, but using the same preamp circuit structure. I think he is already accepting orders on his website and it should be available in a few weeks. $179, including an internal li-ion battery that should run it for ~20hours. This could be another option -- again, do some searches on ts.com to learn more about it.
All that said, since the C1000's are battery powered, you may well only need the proper cable (2x XLR > 3.5mm stereo mini) and you'd be all set. Pretty good feedback on the quality of the mic input on the M10.