i would go the cheap JR/500 way as well. you wont loose money on it.
personally i dont think that the 505 will do much to the cheap JR/500 market when they start. it may reduce the price of a few of the newer ones that are still up there, but you are comparing a new $1m helicopter with a second hand $500k heli. And the 66 has already dropped into that market...
I think that the 505 will hit the 66, EC120 and cheap 350/407 market more, as it is about in that price range. the 350/407 market should be less effected, as if you were looking at a 505 or a B2/3/407 for the same money, i don't think that is a fair comparison, the only similarity would be the price. Totally different aircraft.
Buy a JR from your local Bell Agent, then take it back in 3-4 years to trade it for a 505. tell them that's your plan, should make them even keener to look after you!