Basically I am doing work as a freelance writer and would like a place where clients can log in, request a quote and/or pay invoices sent from the same software. Something that has the buying of credits would also be nice. I have been trying many of the open source and checking demos of paid software and am having a hard time choosing. Really don't want to spend much more than $20 per month but that is open. I use paypal but most scripts will have that option easily built in. Hosted options are not required as I can afford and configure SSL. Uploading and delivery of writing projects doesn't necessarily have to be through that software. Any suggestions would be greatly appreciated.
Have found a site reviewing 10 online invoicing tool, have a look at that site. Hope it would be helpful for you to select right one tool.