Ran a loop of 3/4" RapidAir Maxline today. A kit with all the fittings (less the chuck) for three drops and 100' of tubing was $200-ish.
VERY nice stuff, the air blocks are nicely machined out of billet aluminum, all the fittings are either stainless or brass, and includes drain valves at each drop.
I was a little worried about bending the tubing without kinking it, but it turns out the 3/4" conduit bender I bought for the electrical work is perfect for that.
If I was going to run a LOT of that tubing, I'd make or buy the straightener for it (it comes coiled up) but I managed with a 3 foot piece of appropriately-sized PVC and the trusty Beer Belly Clamp.
Still waiting on the electrons, hoping for this week coming. Pretty much everything else is done, less the furnace. Keeping an eye on Craigslist for that and if it doesn't happen by cold weather, I'm pretty sure my propane salamander will git 'er done as well insulated as the building is.