If you have a recent appraisal on your property then all of that information should already be in there.A complete summary real estate appraisal on an income producing property will have three parts: Cost Approach, Sales Comparison Approach and Income Approach.The Cost Approach will tell you what it would cost to rebuild the property, less depreciation, plus the cost of the land.

My question is, what is a reasonable rebuild cost for a single family row home in Philadelphia with mid-grade finishes?

If you're talking about plumbing and electrical it's a completely different ballgame than repainting inside/outside, rebuilding a deck, putting in a new countertop, etc.

I have some idle cash and my builder friend wants to rebuild on lot I purchase. 

@Alec Anderson, it is too much of a legal liability if you ever say the property doesn't need flood insurance because if it floods and they don't have coverage it might come back to bite you when people are desperate and have to figure out how to rebuild after a major loss and a flood loss is costly.

If the bricks have deteriorated or the mortar washed out, then you would be heading in the direction of rebuild/replace rather than repair.You should probably consider having a foundation specialist and/or structural engineer examine the foundation and provide you with an effort and cost estimate for repair/replacement before finalizing a purchase of the property.

Same as residential, look at the income it produces and what it is worth, look at comparable sales and look at what it would cost to rebuild it.How to find out what it would rent for?

Something like that.My problem is, I've never hired a contractor before, nor even used a hammer, and the only time I've used a drill was 6 months ago to drill into plant pots for drainage holes.I've had a GC contractor and quote me a price that I could literally scrap the house and rebuild the entire thing, it was so expensive.Could I have a rehabber here in vegas, come over, look at the place and tell me what they think it should cost, how I could pick up a hammer, try not to hurt myself, to cut down on labor, and estimate how much it should REALLY cost?

I have seen a few where someone has invested a large amount of cash to rebuild them, but these were not for sale. 

I beg you.All new plumbing risers and lateralsAll new windows, doorsAll new furnaces, ductwork, everything related to heatingAll new electricalNew RoofI would strip everything to the studs, keep existing sub flooring if you can (you can lay 3/4" plywood and shim to level if they're off), and rebuild from there.