Hey Claudia,
I think you're a bit low on your offer here so long as your repair number is right. The 70% formula is a bit out of date and really not specific enough when it comes down to it.
I think you're better off itemizing each expense and formulating your offer off of that. The big variable will be how much buyers in your area are willing to accept as a a return on their money. I think 10-15% is a pretty good barometer but it's going to be up to you to peg that one.
Here's how I see the numbers:
$270k sale price
-$15,000 repairs
-$13,500 sale commissions (5%)
-$2,700 in purchase closing costs (1%)
-$2,700 in sale closing costs (1%)
-$2,000 in holding costs
-$6,000 wholesale fee to you
-$33,750 profit to investor (12.5%)
=$194,350 Max allowable offer
This is higher than the asking price which leads me to believe you might be off base on the repair number. Did you find the deal on the MLS? Deals with this kind of profit built in including a $6k wholesale fee aren't usually falling off the trees these days.
If you're sure you have your repair number pegged correctly, then you have room to up your wholesale fee IMO.