For sure you've done a good job with insulation & sealing!
The cost for gas heating seems very reasonable around here,
but they never laid the pipes in this neighborhood.
For the most part, my neighbors are all dependent on fuel oil for heating and DHW.
Even with the mild weather, they are getting hit hard in the wallet.
Yeah, you should make an effort to exploit solar space heating as much as possible.
Looking for the right size glass, while you build the collector(s) seems like a good idea.
In the interim, you could just use plastic sheet.
Like the heavy duty 48"x25' stuff I found at Home Depot.
48 in. x 25 ft. Clear Plastic Window Installation Kit-V4825/4 at The Home Depot
http://ecorenovator.org/forum/conser...html#post16999
It's pretty good stuff and might last a few years outdoors..
But it likely require a very steep mounting angle, to let the snow slide off..