IMO I would definately get a water test kit. Even if you're doing water changes you don't really know how the water is until you test it. My tap water for example is on the high side of the Ph scale so I like to make sure it doesn't go off course too much. Its your fishes health and he/she relies on you to do it right. Everyone has their own opinions on water changes and testing but I would highly recommend testing your water at least once a week. The vacuums are good for getting all the poop and old fish food (if it falls to the bottom) out of your tank. Its easy to do and takes no time at all. The water test kit I use is this one:
it's a bit out of your price range but is highly recommended by many people here. You can get individual test kits for Ph, Ammonia, etc but the kit is obviously cheaper than buying them all separately. At the least I would get the Ph and Ammonia ones. Good luck.