At work we feed ours hitchhiker crabs, the occasional emerald, cubes of frozen mysis, and even peppermints if we have thousands in stock and a couple are looking dinky. If you ask your LFS for hitch hiker crabs chances are they'll have some.
You can also ask for "fake emeralds" none reputable distributors will send these out as emeralds and they're just crabs that get huge from the atlantic so the stores wills sometimes give them away.
If all else fails, tell them you need to feed a mantis and that you need a sweet deal on crabs.
Since you're in colorado springs you should hit up Jonathan Bush if you haven't already and I'm sure he can help get you some live food at a good price for the mantis.
Tell him Claudia sent you, he'll help you out(although, I'm about 75% sure you got this guy from him)