The cheapest way to do it is to get some NCR paper off Ebay. The ones with yellow and white sheets of paper. Design a invoice on your computer with logo ect, then print on your NCR paper, but remember to print on the correct side as it will only work on one side. Get yourself a clipboard and a A4 size piece of card, put your sheets in alternate yellow,white on the clipboard starting with white and just put your card under the first 2 sheets of paper (under the yellow). What you wright on the first white paper will transfer onto the yellow sheet. You keep the the white sheet, the customer gets the yellow. The only thing with this system is you need a container on the van as you will end up with a cab full of invoices everywhere.
There are loads of companys who will do a NCR book for you, but you will find it will cost you a small fortune, when you tally it up at the end of the year, especially for colour ones.
I don't use paper invoices now for domestic customers, the lad who works for me just tells the customer if they need a invoice to contact me, and i will send them one by email, not many do. I still create a invoice for domestic customers, just not on paper. I keep the invoices in folders on the computer, flash drives and on a online cloud storage, so they can be printed off at anytime.