Not sure about non-US law. In the US, you would need to register as a federal money service business (MSB), as well as in all 50 states (it costs about $150k in state level fees to do so). In addition to this, it is (from my research) incredibly difficult to find a bank that is willing to touch you with a 10ft pole. When they are, they usually charge high account maintenance fees (one bank told me 10k / month) due to the increased record keeping they need to do.

I agree that there is a massive need in this area. It is total non-sense that every online transaction costs 30 cents + 2.9%. I think it is very much a reason why the whole internet is still ad and tracking supported. It is not possible to bill people near the true cost of computation on an incremental basis.

It very quickly turns into a money launderer's dream. So I understand the regulations, however, they are incredibly burdensome and feel anti-competitive (re: banks). The best thing to build it off of is ACH, so if you go this route you're looking for the cheapest ACH provider you can find. It does make sense though, one ACH charge on the deposit and one on the withdrawal, which enable a lot of (free) transactions in between. It could save a lot in the fixed costs (the 30 cents part).

I'm talking to a lawyer next week about some exemptions to see if a C2B play makes sense in this space. P2P is hard (in terms of regulations) and you're probably best served by cryptocurrency. That too may fall under MSB laws, so it is best to talk to a lawyer.