No need to buy another buffer solution, those will work. I've calibrated to all sorts of solutions before, commercial bought and lab made. Readings are the same so long as the calibration is done right. Buy a meter with ATC and readings out to .01 if possible.
Also, $20 for 3 of the 65 ml bottles? Good Lord, that only costs a few dollars to make and you need barely high school chemistry abilities and instruments. It's like $30/gallon wholesale. Oh well, good on them for trying to stay in business, I suppose.
[edit] for autocalibration, the meters are usually programmed to use a certain reference solution. That varies with the part of the world you're in. Also, you can usually calibrate manually.
