I have a friend who also has a Marathon.  I haven't seen it yet but apparently these small stone mills were made by the Mormons.  She bought hers 25-30 years ago for about $300.  She says it always worked well and never needed maintenance.  And a blog I found also indicated the same consistency and quality for the (they had used theirs for about 10 years) Marathon they had.  There are no current manufacturers of small stone mills that sell for less than $2000, if motorized.  The price  for the Marathon is a deal, if you really want a stone mill.  I have my own stone mill, a Meadows,  that is also 30 years old.  I just had it s stones "dressed" and the flour it produces is outstanding!

I don't know the size of the Marathon mill. If it is a larger mill (that, for example, need to be bolted to a countertop) $300 sounds fair. Would you compare it, for example, to the Retsel mill?

If it is a smaller capacity  mill, the kind enclosed in a small cabinet that can be placed on the counter and will hold max 1-2 pounds in the flour receptacle, then maybe you can get the price lowered.

FYI, there is a nice, motorized smaller adjustable stone grain mill on sale right now on eBay. The link is http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=290321072320

The mill on eBay is missing the grain hopper - the hopper for this kind of mill is simply a large funnel. I think you could find a replacement.

You should at least check it out if you want to get a feel for the going  price.

I have 2 that I use for my small bakery, I love them.  I know they haven't been made since the 60's by the Grover Co.  But they normally go for around $100 on Ebay