Has anyone found a good source for electronic/esign contracts for customers? I'm cheap, and the ones I've found so far charge $20+ month ... more than I am willing to spend.

At this time, I'm sending the contract to the client via email and asking them to sign it and return via mail/fax/scanned email. My main problem is some customer have problems viewing the PDF on their smart phone, plus, I have to wait for the contract to arrive via USPS.

I'd love to hear what others are doing!

I'm not using an e-sig service right now, but I'm definitely interested. Have you looked into HelloSign ?  Once wedding season is over I want to try it out.

AI simply type "payment of retainer constitutes agreement to contract" where it would normally be signed. Not real concerned whether it's ironclad or not. They see contract, pay retainer, I forward final contract with that bit filled in.

I attempt to get a signature mailed or scanned and emailed.  If I don't (rare), I don't worry too much about it.  Their deposit and final payment is indication of their accepting the terms of the contract.  I had one bride who wanted to change some of the language of the contract.  fine.  They loved the cake and recommend me to everyone.