you can get them at Bass Pro, Cabella's and a lot of other places for around $20 bucks - cheaper than you can probably make your own.
I found another site
www.fishinglightsetc.com that has "high-end" submersable tube lights with replaceable halogen bulbs. $30 gets you three colors and a spare bulb. Even if you don't buy from them, their site has a lot of information about the different kinds of fishing lights.
As for "Evening Secret"... talk about a classic scam. Lots of hype, no pictures and no details beyond the fact that it connects to a battery.