Maybe just run a few financial lead offers with your better publishers/advertisers? If you keep it small it won't require much to get it going.
Get cheap software (not network). IME, financial lead buyers will gladly pay weekly and the pubs will gladly get paid bi-weekly.
After a successful campaign or two perhaps you will have the cash reserves to build a bit. Take baby steps.
A lot of folks here relate everything to copeac type networks but if you are doing financial as a niche, there will be little to no "float" and much, much less legal headache. Dealing with fraud is the big issue, but if you say you have trusted pubs....
good luck!