This may sound old fashioned, but a lot of the tradesmen I have hired have worked for themselves, and their wives, who had also worked the trade and understood it, did the invoicing, accounting, customer calls, etc. Teamwork for the win!

One of my projects is open source (and more importantly, self custodial - not SAS) accounting tailored to the tradesmen who have told me their troubles in that vein. E.g. printing invoices in the field is a win. Not all customers are happy with email, and you need a signed paper. And if you hand write the invoice, then your wife/accountant has to double enter it.