All wheels can go out of true soon after being built. Machine built wheels, which all budget wheels are and many better ones, will go out true even faster. It's just the spokes settling in and a quick trip to your lbs will see them nicely adjusted and trued and ready for action.
As for cheap - you get what you pay for. Buy cheap, you will get cheap wheels. If you're on a budget, and already have wheels, you're better of talking to a wheel builder about what he can put together for you - firstly because he may have a better choice of bits but mainly because the secret to a good wheel is not the hub or the spokes or the rim, it's how it was built and tensioned.
For my money, you've got wheels that are working. Get them checked if you notice wobbles or creaks, otherwise ride them until you can afford some good wheels.
Richard