I've done that with a propane burner, gently heating a PVC tube to get the correct bend. I did that for underground water piping for irrigating my garden. Connectors do add up to a lot when doing many connections.
I had a greenhouse a long time ago that fell apart so I tossed it out (rusted metal pieces). I figured that if people own 3-D printers, why not put them to use to make the connector pieces. For a structure, you're not concerned about making a watertight connection, just something strong enough to hold pieces together under load. Should be relatively easy to create designs that minimize amount of material printed that gets the job done.
I'm planning on buying a 3-D printer soon. Just trying to figure out what I'll create beforehand, in order to decide which model to buy. PLA is easier to print. But ABS is stronger, more flexible, doesn't break down as easily however it is more difficult to print (warp issues).
If you want to start inexpensively, build your own 3D printer. Here is a recent article.
http://www.computerworld.com/slideshow/detail/128090
“5 cool 3D printers for less than $500”
Though not mentioned in this article, I really like the Rostock/Delta design. Steve Graber’s “Cerebus” looks great and affordable. You can build it to print with ABS, PLA, Nylon, Carbon Fiber filled filament, Wood filled filament, etc.
https://www.youtube.com/watch?v=lmuobEa7Tt8&list=UUn8_8lCxnFYEPLXFlKSxRCQ
https://github.com/grabercars/Cerberus
Steve uses the magnetic ball joints developed by Werner Berry. Very innovative!
https://www.youtube.com/watch?v=x6PLHl0HHq8