Depends on your definition of cheap, and what you're using it for.
High power systems are plain expensive, even to DIY, but DIY is far cheaper than commercial and not insanely hard to do. However they make the most sense in lifespan and running costs being far better than the alternatives if you want a lot of light.
For lower power sets you still get the lifespan benefit and reduced running costs but it takes longer to notice the difference to offset the convenience and price of the basic sets.
If you're looking for lights for a non-planted set then you're probably steering towards some of the sets from e-bay, or using some of the waterproof led strip or ribbon lighting that's often found as accent lighting for kitchens and bathrooms.