I got mine off of ebay for $20, but you do need to get the calibration oil, which is super cheap, like $3ish bucks. Get one that is 35 ppm or calibrated for saltwater.
Yea they are not much, and do last a lot longer. Just get a new one t hats about or just under 50 bucks and you should be fine :) mine was about 50 AUD