I'd recommend eCS, but based on Playstation 2 discussions in the past I know $330 is not exactly in your budget.
I picked up a copy of Warp 3 at [link|http://www.halfpricebooks.com/|Half Price Books] a couple years ago for $10.
Also check ebay, I understand OS/2 shows up fairly often.
I'd also highly recommend you get [link|http://www.prismdataworks.com/warpup/|WarpUp!] as it'll contain all of the available "free" updates to OS/2 as well as a nice front-end to see what you have/haven't yet updated(there's seperate updates for drivers, TCP/IP statics, the base OS, etc).
Yes, 4.0 has the right drivers. 3.0 came out when there were lots of ways to hook up a CDROM. I had the driver problem with 3.0, my CDROM was hooked up via a sound card's proprietary connection. Luckily I had internet access at U of H and was able to easily get the updated drivers.