After searching fruitlessly on eBay (because there is no other option) for a 51 in dark blue with gold cap, I was just about to give up on ever finding a 51 that I might enjoy. Then this popped up on the classifieds:

Now that is a model I could accommodate in my literal handful of pens...

… alas, this also seems almost impossible to find in this condition and at this price (it was $115).

So, in today's market, and ignoring the price-inflators that populate eBay, what are the frequencies of the various 51 models that can still be found at sensible price?*

*not talking about super rare things here.