i got mine off of ebay. I have a pH pen and a TDS pen, not a combo deal. The pH Pen was $30 and the TDS was like $15. here's what i have and they work great:

pH: NEW DIGITAL PH METER FISH MARINE AQUARIUM, HYDROPONICS - eBay (item 380039909803 end time Jun-29-08 18:38:08 PDT)

TDS:
HANNA Primo TDS Meter, PPM Tester, Conductivity - eBay (item 270248851582 end time Jun-29-08 13:25:30 PDT)

good luck
Skeet
elskeetro Reviewed by elskeetro on . where can i get a not so expensive EC/TDS tester? Ive been looking around and trying to find one that isnt $100+. Im just doing a small 1 plant W/F grow so do I even need one that bad? I see stuff in here that indicates just following instructions for the GH 3 part or Latewood's recipe with R/O water, calmag+ and LK and it should be fine. Then I see others expressing the dire necessity for a ec/tds/ppm meter. This is my first hydro set up so theres a huge learning curve that im trying to accomplish without asking too many questions. Rating: 5