Guys...
Forget about alternatives.
Glass RULES..... Otherwise, plastic mirrors would have been here a long time ago.
The only so-so alternative is thin aluminised mylar and low pressure round chamber behind it, where if placed as cover it will form paraboloidal surface. BUT, the shape is subject to pressure differences and this works only for far IR, where departures from required shape are comparable or smaller than wavelength.
Another one may be speculum (alloy that people used for mirrors in the past, but it does not compare to glass.
Try
www.surplusshed.com or similar places, there you can find cheap mirror.. the rest is , as you said, next to nothing.. except time and fiddling with plastic tubing and other parts and materials from Bunnings or places like that...
For finder (and eyepieces), use second hand binos, you can find them for $10 on Sunday markets...
And, besides, what is wrong with binos to start with?