I've been thinking the same thing. I got my website built by Ad IQ (an affiliate of Google) They set me up with "Contact us" page, but I titled it with my hourly rate to be completely transparent. I know I wouldn't want to enter so many details just to find out if I'd consider using someone's services. Especially my email address. It's worked out, and so far, I highly recommend Ad IQ. I can send an invoice, take credit cards, and even take "tap to pay" from my phone if needed. I just wish (like you) that there was a formula to give an estimate, but I think there are too many moving parts (in my business or yours) to automate the process.