Hello Austin...You should really do some research on R/O units and how they work to benefit your needs in this hobby.
You will find that they consist and plastic canister tubes and lines that run in into each other but the true guts and most important are the filters.
$300 is a reasonable price and can get a complete unit for less if you shop around.
Depending on your application, you will have to determine how much r/o you will need which is measured in GPD (gallons per day)
As for lowering ph...don't worry about that as heard many times here on SD. Keep it stable which is recommended.
...Ralph