There are Linksys SIP compatible IP phones that have much of the functionality of their parent Cisco models. I would suggest determining the technical needs of the network and compare models.

These Linksys models are about $100 cheaper per phone than Cisco models.

I agree, Linksys is probably your best bet. They are one of the more cost effect options and widely supported since they are so common.

Here is one site that has volume discounting on Linksys phones as a possible source for you.
http://www.altoedge.com/ipphones/index.html

The Polycom 550 is one of the most popular phones on the market. I would recommend that. Also, the 330 is a very good phone. You can find more info on the phones here:

http://www.freedomiq.com/voip-phones/

Also, here is an excellent phone comparison chart:

http://www.freedomiq.com/voip-phones/compare-voip-phones.shtml

However, from experience, I would say that the 550 is the best bet. You can always buy used phones too if you want to save money. You can also utilize a softphone. Here is a link to more info on that:

http://en.wikipedia.org/wiki/Softphone