Automation of Invoicing between Quickbooks and Salesforce

I am looking to automate the invoicing procedures within a QuickBooks desktop application and Salesforce Enterprise for a small wealth management practice. Invoices are currently sent out quarterly from QuickBooks based on custom fields within Salesforce. Activity records are then manually entered in Salesforce with much of the same information. I would like to automate this process and/or develop a more efficient process. I have contacted firms that have annual fees, plus development fees and I am hoping that a good developer can create this automation without the unnecessary subscription cost.