Eric,
I have not used either, so I can comment only on the prices (I bought an M3 last year and I have been slowly getting lenses, so I have been checking prices for some time).
$360 is on the higher end of what is being paid on eBay, but still within reason. (Keep in mind the 1969 Summicron "one of the finest 50mm lenses made") that Justin mentoned above is a different optical design from the collapsible.
I have found a good idea to check the prices at KEH as a guide. They list a collapsible Summicron "Excellent" for $379 and the Elmarit for $275 as "Bargain" (=perfectly usable, in my experience) and $429 as "Excellent".
Everybody will recommend to try to get the newer lenses-- However, I have a collapsible Summitar I got for $176 (+$30 for M-adapter) and I am very pleased. In my case, if a "classic" lens starts to be close in price to a newer lens, I am not interested.
Current Elmarits can be bought on eBay between $450 and $600, Tele-elmarits between 300 and 450. Both are supposed to be better than the older Elmarit.
If you are going to pay a little bit more, you should ask for return privilege or some kind of warranty.
I hope this helps.
Juan