As a freelancer: $35 one time seems fishy to me. If you're asking a one time fee, I would not even spend the time to look at your offer. (which I did not)

If I used your service, i wanted it to stay around and paying one time doesn't give you incentive to keep it up.

Better model:

$35 a year - which renews for free unless you hit a certain invoice amount (for example, if you invoice more that $35000, you'll have to pay again.)

Add a free trial, the first $3500 invoiced are free as a test and you have a valid offering. And you can do unlimited, watermarked tests.

Finally, consider data protection: You need to exactly explain what data you store and that - as a paying customer - I can selectively delete it.