Why are some Mini Z's cheaper than others
 

Is it that they are an older chassis? Why?
Thanks

That's part of it , MR-01's (the first generation Mini-Z) cost less than MR-02's. But MR-01's may also vary in price, even though they're internally the same.

This is usually just due to good old supply and demand.
The popularity of a some shells over other (older) shells is reflected by the price in most shops.

Just that some places have an overstock on a certain readyset that takes up room in the warehouse that needs moved. So to make room they are marked down to clear those out. If the box was opened to put a different shell on they can't sell it for full price anyway. So it's simpler to just mark it down to move it out.

I say if you find a good deal on it, take it. The only thing I can think of as far as a problem would be the wires on the board may be brittle from setting around for a long time.

i bought mine factory sealed, bearings , and x speed motor for 130 shipped from japan..i think that is one of the best deals available

One note, however - there are a lot of FAKE Mini-Zs around - these are in no way compatible w/ regular Mini-Zs and should be avoided at all costs, they are not worth any money at all. If you see anything for $5-50 on eBay and it looks at all suspect, don't buy it. Real Mini-Zs will pretty much always be in the $90-180 range. :)

The cheapest I seen a "Kyosho" Mini-Z is 85$. That isn't the palm runner (There cheap as well). Like Tiny RC said there are alot of fakes out there. That 85$ price is like a rare deal. If it's don't say Kyosho stay away from it. Unless you want junk to trash.