Hello! I'll not bother you by stating my experience and related projects, so we can go straight to the point. I believe this is a rather sensitive and complex (we're talking about your finances), so it'd be silly to do it in 7 days and for $300, this should take at least 14 days and $400. If you agree and want it properly done, let's go with the proposal itself:
I've done this previously using a multi-chain approach (TRON, SOL, ETH & BINANCE) and know two ways to achieve it, the first one uses Blockchain Explorers HTTP API which it's useful to verify payments using a QR only. The other one uses Wagmi JS along with React.JS which enables account creation, transfer and multi-chain verification. The former is limited to verification yet it's faster and cheaper to develop, the latter is more powerful, real-time yet more costly.
Now to the boring part: I'm a Developer with more than 10 years of experience with Web, Mobile and Cloud. I own a company which can provide you the needed security of: digital marketing, service contract, NDA and affordable ways of payment.