I would pass on this deal. There isn't enough spread in this for any errors including the property taking too long to sell.
I am also very suspect of your estimated holding costs of only $1000 if your expectation is a six month hold. You will have water, electricity, gas?, vacant property insurance (unless you're going to risk it), and pro-rated real estate taxes during the rehab. Is any of that included in your rehab costs because $1000 holding cost doesn't cover all of that.
Also, are you planning to sell to an end buyer or an investor who doesn't want to do the rehab himself? If you're looking at an end buyer, someone who can only afford $45,000 for a house is likely to need a lot of help to actually get in. You may end up paying ALL of the closing costs just to get the deal done. On houses this cheap, I estimate 10% closing costs.
I always back into the most I could pay for a house using my desired profit. I'd want to make $15,000 minimum to split between you. Any less and you have no room for error whatsoever. Here are my numbers (not having seen the deal, obviously):
Sale Price: $45,000
Desired Profit: $15,000
Closing Costs (out): $4,500
Rehab Costs: $7000
Wholesale Fee: $1500
Closing & Holding (6 months): $3000
Max Purchase Price: $14,000 cash
Good luck with this one. I just don't see the numbers.
If you still want to lend the money on this deal, I would go in strictly as a lender and not a "co-investor", and I'd get additional collateral because any mistakes by the guy who is actually doing to the work could cost this deal all of it's projected profit in a heartbeat.