Here's what I see. $35/bundle x 4 bundles per square. 600 sq foot house + shed + overhangs, I'd overestimate the sq foot of roof at 800. Shingles = $1,120. 2 boxes of roof caps at $100. 4 rolls of #30 tar paper at $100. Looks like one valley + five stacks/vents to flash = materials about $80. 130 ft of drip edge flashing at $50. 2 coils of nails at $60. Roofing tar/caulk = $70. Let's say $1,600 for supplies. Dumpster $150ish. So total less labor is $1,750. Looks like a 2 day job with 2 men. 32 hours labor at $20/hr = $640. $2,390 all in + $1000 profit = $3,390. Give a 20% buffer and that leaves $4,068. That's what I think a fair price is.
It does depend on how far it is to the roofing supply store, how far it is for the workers to travel, if there's any rotting wood that needs to be replaced and how busy they are (busier = higher profit).
You could buy a couple ladders, a compressor, a 100ft extension cord (14/3), 50 ft of rubber air hose, a roofing nail gun, a caulk tube a couple shingle removers and pick up some day laborers who know how to roof. Get the trash company to send a dumpster, rent a truck to get the supplies (or pay to have them delivered) and you're set. Just make sure you have enough insurance, just in case someone gets hurt.
And your existing roof looks pretty good, so I'm assuming you're replacing the roof due to leaks. If that's the case, you should be able to repair it, without replacing the entire roof. I also don't see three layers of roof on the house, but I'm going by the photos and it could be there.