What % of a deal is a co-signer worth?

[John Beede]

I've studied, researched, scoured, and found and great deal on a flip. Numbers are all very good. I've got an 800+ FICO score and I'll be doing (or overseeing) the rehab. I'll also be handling the resale. Only problem? I have a high debt-to-income ratio because my other investments are in my personal name. Banks and private lenders therefore want a cosigner. I have a family member who agreed to cosign... but wants half of the profits, stating that the deal wouldn't be possible without the work they've done to help qualify.

This doesn't strike me as fair. Am I being greedy? Is cosigning really worth 1/2 of a deal?

If not, do you know of any other methods to find a less expensive cosigner? Thank you.