I used to do Xboxes, and I now do 360's. It's not very difficult work, but it is dangerous. There are many dangers since IF they provide the service, when you read their little Terms of Service, you'll most often find they do not warranty their work. From a book-keep's point of view, that's not a smart move anyway if you're breaking in new staff, or having a bad day since you're maybe making 100 dollars for 10 minutes work on a 300+ dollar console. One screwup may be acceptable, but more than that cuts a day's profits down to nearly zero. Can't have that..
Anyway, onward. You're better off doing it yourself, unless you know an engineer or trust someone who has experience with a soldering iron. I'd never trust anything online like that, because if you pay them, and ship them your console, they have NO obligation to return it anyway. There's no contract involved and there is no work order. You're basically on good faith. Not good practice.
Also, It's not a good idea to mod the wii anyway since it lacks versatility from the get go. What few features you could add wouldn't be worth it in the long run, because I know HOW they're going to check for modded consoles and it's going to be very effective. The discs are checked for authentication with a checksum of bad sectors. Each disc is different, and the wii can log these. Even if the modchip can scramble the fake codes for the discs, it can't keep it compared to Nintendo's original list, since they can change the hash code at any time with an update.
Overall, the wii's fine on it's own. If you don't wanna spend money on the games, rent them instead. S'not like there's a MASSIVE count of games yet, roughly estimated at 90-ish original games for the Wii, with I think around 20 more around christmas. I myself am waiting for Nights into dreams, because I fell in love with that game on my saturn, which didn't survive something that happened years ago.
That's just my views. Opinions and experience differ.