I"m in the same boat with my H. tatauaia. Many LFS are willing to order a large bag directly from their suppliers. Approx 750-1500 guppies/bag (depending on quality ie fancy vs "regulars"). Anywhere from $50-$60 depending where you go. Make sure to talk to the owner of the LFS and not employees. This way you pay 1/3 to 1/2 of what you are paying now. You will need a larger CYCLED quarantine tank......and poower feed. Quarantine min 2 weeks to 4 weeks to reduce chances of transmitting any type of disease.
Yoiu may also consider gtetting a pair of convicts. I am currently trying to get a pair... once you have a pair, they produce fry like crazy. Since you have many fish you feed, 2 pairs would be even better. (in seperate tanks).
Try to get your fish off live. The ONLY fish I have owned that has refused to eat non-live in the past 4 years is a tat I currently own.