I'd get out and look at Glocks and watch the local ads since used ones do turn up. People always are wanting to sell to go to a different caliber or model or even lately to move from older generations to Gen 4. You never know what will turn up. I recently bought a used G27 for a real good price. I'd planned on buying a Gen 4 G27 later but the price on this Gen 3 was too good to pass on.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek