Suggestions for simple "auction" feature?

I have a client who would like to incorporate a simple auction feature into her site. She holds charitable auctions in which she’d like bidding to be possible both on and offline. Because of this, the site won’t be handling any monetary transactions; it just needs to accept bids and display the latest bid.

The simplest solution is moderated comments; but the comment area would need custom fields, and it would need to be distinct from other comment areas on the site.

A more complex “perfect world” solution would be a function that accepts field data and outputs the latest AND highest bid.

Can anyone think of a plugin, script or WordPress function that might work for this? I’m much more of a designer than programmer, so any help is appreciated.