can try Petmart....they're selling one of the pH pens for $65.
I bought the Aquasentry for $140 from them. monitors both pH and temperature simoultaneously. I know its a made in Singapore brand and that probably nobody has heard of it or used it, but yeah, thats not stopping me from buying it and trying it out. if you want a review, don't bother getting one from me yet coz...my tank is not ready yet and I can't use it yet if my tank isn't ready right?