My first choice would be (as already stated) the Kayfun lite + clone by either EHPro or Hcigar, but they are usually a little over the $40 mark unless you get one one from
fastech.
My next choice would be the Aqua clone by EHPro and it is within your price point.
The Aqua is a great RBA but I do find it to be a "
juice hog" and I wish it held more juice.
Edited to add... The Aqua does have some advantages over the KF style tanks though - duel coil (if thats your thing), adjustable juice flow, and you can recoil or rewick it without having to drain the tank.