These things used to be everywhere. Can't imagine much demand. But I'll say probably $10-15.

Cool, thanks.  A local used bookstore had one for $16.95, glad I didn't take them up on their "discount" =)  However, I did get a Runequest 2e rule booklet in VG+ condition for $6.95 (those go for $20-25 on eBay).

I'm very inspired right now to look for great deals on places other than eBay.  You guys have scared me away from there =)

Depends on which one it is.  There are two Red Steel box sets, if you weren't aware:

2504 Red Steel Audio CD Campaign Expansion, Boxed Set
9500 Red Steel, Savage Baronies Audio CD Accessory

I would suspect that a lot of time people think that the 9500 boxed set, which usually goes for $10-15 in SW, is the only one.  The 2504 boxed set is usually harder to find, especially in shrink.  I would suggest that it is worth a little more than 9500, perhaps $20-25.