The supplies are really starting to dry up, this is reflected in the price. I too saw new original Renault chassis' advertised in the Dutch R4 club's magazine for about 1500 euros like Liesje mentioned. This, however, was almost two years ago. If the price is still the same, I'd say it's a bargain.
I happen to have the Renault Dialogys parts programme with prices(dating from the beginning of 2003) on my computer, and this is what Renault wanted for the chassis in France then:
2585.56 euros!!! VAT not included!
That was almost two years ago, I do not have the latest info if it's still even available from Renault. Maybe the company that advertises the chassis in the Netherlands has bought several chassis' earlier and can therefore still offer them at such an affordable (compared to Renault) price.