Well, I've never seen a new one, but here are a few benchmarks from my observations on ebay since May 2005.
The lowest I've seen U.S. Magical Chase go for was $175+/- with manual but no box in 06.
The most was around $1,000 with box in '05 or '06.
I haven't seen many with the box lately. Loose cards have been closer to $300; cards with manuals have been closer to $500-$600.
In the inflated Buy It Now realm, complete PC Engine versions are around $160, up from $125 last year. This doesn't mean much, but might indicate that general interest in the game is up (or the sellers are just bigger a$$holes).
A possible comparison might be Reg Frog's sealed copy of Dynastic Hero, which he seems to have sold for $800 outside of ebay. Of course, MC is probably more valuable.