PM me if you would like my email. I have raised guppies on and off since the 1970s. Only recently getting back into it. I can share some info sources with you.
Keep in mind I am not telling you the BEST way to raise guppy fry in this thread. I am telling you how to do it without spending $100 right now. If you enjoy this, you'll want to work towards a better setup. I currently raise guppy fry in a 5.5G tank, with heater, filtration, a few live plants etc. A goldfish bowl is never ideal, but it's workable for a temporary situation if you do the work of keeping the water clean. Guppies can put up with some abuse, but there is a difference between thriving vs just surviving.