I think I would have most experience to talk on the matter since very recently (a few months ago) I went thru same exercise with my friend from there. He was lucky to find some who wanted to sell his Sunfire HRS-12 sub - this one:
http://www.hometheater.co.il/vt238263.html
Final price was 2750 nis with pickup from Akko
It know it's out of your $500 range, but Israel is no US. Most subs are around double their USA prices
In general in Israel market is very limited and finding good cheap sub is very challenging - practically on oxymoron.
Custom Importing is also expensive due to high import tax and dues.
Also Try to find this sub: JBL ES250PBK
Bottom line : You need to really patient. Out of your list probably Focal/JMLAB SW700 would be my pick.
http://avforum.no/forum/tester-audio/48883-minitest-focal-jmlab-chorus-sw700.html