what is the best place to purchase internet cable modems?

Hi there.  You can find a Linksys CM100 Internet Modem on several websites.  You can buy them new or refurbished.  Let me show you just a couple of the deals I found for you.  Let's start with the new modems, okay?

http://www.amazon.com/Cisco-Linksys-CM100-Cable-Ethernet-Connections/dp/B000WIK61I
Brand new cabled modem from Amazon will cost you $64.99 and you can get free shipping with this offer. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16825120001&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Modems-_-Linksys-_-25120001 Brand new cabled modem from Newegg for $64.99 and free shipping.  Newegg and Amazon both have reviews on this modem too.  Most of the people are happy when they buy this modem.

Now take a look at the refurbished.  Most of these are no refunds, so be aware they maybe cheaper but they may end up biting you in the rear end. 

http://www.buy.com/prod/cisco-linksys-cm100-cable-modem-with-usb-and-ethernet-connections/q/listingid/70284061/loc/101/204240300.html http://www.Buy.com has the modem for $39.98.  This includes the shipping price added on.  http://www.Buy.com doesn't have anything saying they won't take it back.  I would ask though before you purchase it and get it in writing.  You can never tell when people will try messing with you.

http://pcdirect.com/licmcamowius1.html
PCDirect has the modem for $27.95 and free shipping. It is the cheapest I found it for.  They have a warranty for 90 days.  So if you don't care if it's refurbished it will save you a couple of bucks going this route.  I hope this helps you out.  Thank you very much for your question.