Thanks for the replies everyone! I have looked a little at e-bay, but I've never actually purchased anything from it before, so I'm still a little nervous about it. (also - and maybe this is my Dutch blood coming out - by the time I figured in the shipping and handling, the tops I saw would still cost me $20-25, which is a fair bit for something second hand!)
I'm going to check around at the local department stores a little more carefully. I've never seen nursing tank tops there, but I haven't really looked yet either. Maybe if I start asking around here, I'll come up with some good sources. BTW - Target is not available in Canada. But, I am only 20min from the US border, so I could go check it out.
Anyways, I'd still love to hear from anyone with advice or suggestions. Thanks!