search tool for our site?

I would like to add a search field to our website. Can anyone recommend a tool that would be affordable that could index a smallish site. We have HTML, MSWord, and PDF files we would like to index. And I would like to be able to manipulate the look and feel of the search form and the results pages. And it has to work with IE and Netscape going back to versions 4.0.

Any suggestions?