surprisingly, you'll be able to grow many medium to high light plants using clamp lights.
i have 2 8" clamps over my 5.5 gallon and 3 8" clamps over my 20gallon high tank.
6500k CFL bulbs sell in two packs at lowes and home depot for roughly $12/2 bulbs. clamps were anywhere between $7 - $9 each... well within your budget.
If you want things interesting, pick plants with a combination of lighter and darker shades of green. Personally, i have many small tanks and prefer smaller delicate leaf plants to help with the perception of a larger tank.
combine this with a cleanup crew (MTS, bladder snails, ramhorns, Shrimp) and you pretty much have hours of enjoyment ahead