how cheap is cheap and how many do you need? Linksys PAP2T's are cheap brand new here in England and us Brits normally have to pay a premium price for anything vaguely hi-tech.
they can be got brand new about $50 in your country according to this price comparison site, maybe one of these lot will do you a deal
http://www.shopbot.ca/pp-linksys-pap2t-linksys-price-19321.html
I have also built a PABX for the family business, and we have used PAP2T's for the analogue phones for over a year now without trouble, and at least you are getting the guarantee etc. I've found these to be the most painless ATA's to deal with and configurable for progress tones etc (which is important in my case not being in the USA..)
I am on this mailing list for some old boys who collect and restore telephones and PBX's - they do get ATA's cheap via ebay but I wouldn't trust the family business to s/h stuff like that. even then they tend to be PAP2Ts or sometimes sipuras. And if you need loads of analogue sets (i.e more than 8) might be cheaper to buy a channel bank of some sort anyway..
that said I do have a more traditional hardware/electronics/analogue comms background and I would rather spend a bit extra on robust / tried and tested hardware than chance it...
actually if you have CKTS in Canada their community is often a good source of cheap telecoms kit as well as VOIP stuff (the whole community is based around integrating old and new telecoms kit)
http://www.ckts.info/