Thats the worst way to try and figure out your own budget though ;)
Why not start with something simple.
* Gather your core products
* Create campaigns for these
* Track the conversion Rates
* Find your "profitibility" mark
* expand it to more products
* Trend it out another month or 2
Then apply what you have learned in your test cases to your entire catalog and you will have an idea of your spend vs income and how you have to maintain your marketing to fit that moving forward knowing that nothing will be static but you will have an idea of where you stand.
sorry for the runon haha
Basically figure your expenses, figure your profit margin, figure out your CPC vs EPC and see if its profitable to market that particular item.