You can use shoplights, like you said, they are not very efficient for this purpose, but some have reported good results.
I have found that after a little while with a cheap setup I wanted to switch to a more efficient solution, which costs more in the beginning, but less in the long run. To give you an example: Most shoplights come with T12 bulbs, each at 40 Watts. If you compare that to T5 bulbs, you get more light out of one while using only 28 Watts. Of course, T5 bulbs are a little more expensive, and to make them really shine they need reflectors that are quite a bit more expensive.
In your example, you will use two shoplights with four dim T12 bulbs that will provide very low light in your tank. If, on the other hand, you would spend a bit more upfront, you could for example use two T5 HO bulbs (each 54W) and get a lot more light from a lot less wattage.
I find that in the end, I spend more when starting cheap, and end up having lots of spare parts in the garage.
