Although it is kinda pricey, the reason the game sometimes goes for more is because of the disc art variants and the fact that it came with stickers, a mail away card and possibly more (flyer?). But if you look at completed eBay prices, it often sells completely complete (mint including stickers)for $100 (not disc-only). Judging by the sold prices, collectors seem to value a fully complete copy at $140.
If you only want the box, manual and game disc (and don't care which disc art), you should be able to get it on eBay for under $100.