OK, that was more ambitious than I expected!

The first question is what do you mean by “interface with the internet.” Do you simply need to retrieve some pricing information? (That’s not too bad.) Or are you hoping to have more than one person play at once and to compare their bids? (That’s much more complicated.)

If you’re in the first boat, you can actually do almost everything in Excel. You can fetch the information you need using a web service call. The limitations you face are that a) you need to have some way to distribute your spreadsheet (people could download it, but then they have to explicit “trust” it and allow it to run code), and b) it will only run on Windows computers.

The other option is to do everything in a web page with JavaScript. That may not work for you if you need a lot of spreadsheet type functionality, because you don’t want to try to reinvent all that yourself.

Also, there’s almost certainly a server-side component you would need to write which could range from trivially easy to fairly sophisticated depending on exactly how this simulation works.

My daughter plays a pretend horse auction game on the web — I wonder if that’s similar to what you’d like to do?