You can't get a Pentium processor in an iBook. Pentiums run on the x86 architecture, where as Apples use PowerPC, thus your Powerbook would be a g3/g4. After some quick checking on E-Bay I've found this: http://cgi.ebay.com/ws/eBayISAPI.dll...722671079&rd=1

It's a little nicer than what you asked for, but I'm sure you'll love it. It's a great deal for the price. If you'd like, come on over to my site, AppleReport.com, and ask around. I know there are a few people looking to sell an Apple.

In the spec range that you're asking for, you could probably find a good configuration on eBay for $250-$300.

But MikeAR is right-- you couldn't get a Pentium processor in an iBook, but you can find a 300mhz iBook with 8GB hard drive and 128MB of RAM for about $300 plus shipping easily. However, you won't be able to get the "latest software" on it-- that's a little underpowered to run OS X, which is Apple's latest OS. However, you'd get a great experience running Mac OS 8.6, or even 9.1 on it, and running with the same tools from that "era" (like, Office 97, etc), you'll be in really good shape, and have a nice web browsing experience.