The cheapest lighting will be two 2 bulb 4 foot long shop lights. That will give you about the right amount of light, too, but it will use about 128 watts, and you would probably want to make a wood box enclosure, painted white inside, for the lights, so it would look good. That also has the advantage of using cheap bulbs, but with 4 bulbs you could pick a variety of color temperature bulbs to make the tank look like you want, and it would spread the light out over the top of the tank, so the plants can grow straight up.
In order to keep the light intensity low enough to avoid needing CO2, and high enough to grow plants, your light choices are limited. T8 lights are good for just that situation, where T5 lights aren't. (I don't know anything about T6 lights.) Because the tank has an 18 inch front to back dimension, it is best to have light coming from near the front and near the back of the tank, rather than just from a strip down the middle. When the light comes from just one strip like that, the plants will all grow towards that light making the tank look odd as the plants get tall. It takes at least two T8 bulbs to get enough light, so spreading 4 bulbs across the top of the tank gives you enough, but not too much light, and good even lighting.
Alright so what I ended up picking up was a light fixture that gives me 4 t12 bulbs. I went for 2 bulbs designed for fish tanks and 2 bulbs that are daylight. This will give me 120 watts. I know I will nto be able to keep high light plants, but thats alright with me. Now, is there any carpeting plant I will be able to keep with this lighting?
Marsilea minuta grows well with low light, so well that once it is established it can be a nuisance as it spreads everywhere. I always had some difficulty getting it established, but getting rid of it later was even harder.