It's hard to price these since few sell. Here are some more or less 'comparables'.
A 2 wd YM240 sold recently on ebay for $3550:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7513469439
That listing will disappear eventually so here's a description:
Clean, probably garaged since new. 880 hours showing (1,880??)
2 wheel drive bare tractor, no loader or implements. It's revision level 4, the final version, shown by external air cleaner. That would make it maybe 1981-82??? I wish my YM240 was clean like that!
Previously in the past 6 months two 2wd's with loaders went through ebay. The first went for about $5,500. The second looked thrashed and repainted etc and closed around $3,500. I paid slightly more than that for mine locally, loader included, good mechanical condition but stored outdoors 20+ years and looked it.
Maybe someone else can say what the additional would be for 4wd compared to these 'comparables'. I expect your 4wd YM240D should be over $5,000 plus more for the implements.
You probably know these are the US market version of YM2000 (D) and a ton of those have been imported in 'new-rebuilt' condition in the past ten years. It should be easy to find internet prices for those, as near-comparables.
Hope this helps. Anyone have better data?