There is a very small market, and getting smaller. These used to be a performance bargain, but many used Audi TTs, M2s, Cayman/Boxsters even Camaros have similar or better performance (on paper at least). Plus, all are more plush and could be used as a daily driver. You have to really WANT an Elise for some combo of looks, heritage, light-weight (it really does make a difference), exclusivity, whatever. There are better cars for the price, just no better toys. The market seems to be sitting at about $30K average, less if it has issues/milage, or more if it is particularly clean, low-milage, etc.
Then there's buyers. It has to be yellow, under 25K miles, with a hardtop and for only $23K because someone on the Internet got a rebuilt one for that </eyeroll>. I found an awesome one and probably paid a couple of grand too much, but it was ultra clean and needed very little. So far it has been perfect.