Your question can't be answered- it is a bit like "What is a '42 Chevy worth today?" The value of ANY gun is based on the exact make, model, condition, and originality. A meaningful answer will need a hands on appraisal by someone that knows WW II Japanese weapons. An 8mm Type 14 Nambu in very good condition will probably sell for more than $600. That presumes no parts modified, all markings intatct.
Do a web search in Google, Dogpile, Mamma, etc. and you should come up with some answers. Check out the auction sites, Guns America, Auction Arms, Gun Broker.
50 tops
As of today (01APR2011), One Japanese Yen is worth slightly over one US cent ($0.0119). One US Dollar is worth about 84.10 Yen.
Which one?
For which pistol??
10-100 usd
it is worth about £278/$313.
20
is about 100.00
More information is needed to identify the manufacturer of this pistol.
Colt has never made a 45/410 pistol
Today 2 September 2014: 1 US $ = 104,21 yen