Quoted from ForceFlow:

The polk subwoofer is typically less than $100. And since it's an external box speaker, it's not always very desirable.
The thing about mods is that there are only a select few that are actually valuable that buyers might actually want. A colorDMD is usually the big one. A shaker motor is sometimes desirable, but not that expensive. Otherwise, most add-on mods are going to be subject to individual tastes and preferences, and thus generally have a low value to most people.

Other than the three I spotted, what else is there? What are the extra lights that you mentioned?

What are they?

When you put a higher than average price on a game, there are going to be some questions about what makes it more valuable than other examples of the game.