I used blue xmas light led's. Each strand was 25' (I think) and I bought two strands, which was around $10. It's not like you can see the colors in the fish, but you can still see the fish. My room is very dark. I've seen proper aquarium moon lighting and its much better/brighter, but this so far suits my needs until I can fork out another $100 for moon lights.
I have eggcrate for my top and I pushed the lights down into the eggcrate. If they just layed on top, I'm not sure how effective they would be. Also, I have about an inch of space between the water and the top of the tank and you can see the reflection of all the lights in the top. Once this gets covered by the canopy and you can only see the water, I imagine it'll look better - at least less distracting.
Personally, I say go for it. $10-$15 isn't bad and if you decide you like the look, you can always upgrade in time and use the xmas lights for...decorating during the holidaze.