The bubble wrap will be fine if you run the reflective 3.8r stuff...
Figure it this way..
Wirsbo 1/2" tuing 2 1000 foot rolls $1150
4-500 sq foot rolls of concrete barrier tubing $1750
So you are around $3000 before you buy a boiler, manifolds, circulators, mixers, etc.
If you have natural gas available, I would go with something like this sourced locally..
http://www.ebay.com/itm/Goodman-4-T...530?pt=LH_DefaultDomain_0&hash=item19e9d32202
Look for a dual fuel package heatpump a/c unit...
They work really nice, you will be surprised how little the gas burner runs, and the install is simple in a large open building. Only run a gas line, thermostat wire, and electric service. Then pop the 2 ducts into the building they sit at ground level.
You will obviously have to get the proper size to control your buildings temp, but you will also get A/C. It will be medium efficiency since your heatpump will run most of the season and then the gas burner will kick in on cold days, but since most people keep garages around 60, it is usually very cheap to run...
You can get a goodman or rheem 4 ton, 130K btu-ish unit for about $3000.... Just have to call the local supply houses and see what they sell... Sometimes the internet is a good deal so always check amazon ebay and google after you decide on a part number, make sure you factor in freight and tax...
good luck, I have installed many dual fuel units in garages, they work excellent..