You can create a quote for them right from in the system, then, instead of sending the quote to the client through their email, you can print the 'Unsigned Contract' from the top right of your project.

Then, when your client has signed the contract you can manually move the project to a 'Signed Status' by clicking 'New Project' and move it to 'Quote Sent' and finally into 'Contract Signed'

Finally, you can capture the payment in the Billing tab by selecting 'Capture Payment' and enter in their credit card number and they payment will be securely processed through stripe!