I am not sure why MI:3 doesn't work on the DS, it just is not compatible with the DS port of SCUMM. Probably has a lot to do with limitations of the DS. Perhaps someday they will release a version that can run The Dig, Full Throttle, and Monkey Island 3. It is really cool to be able to carry these old games around in your pocket. What I would really love would be to play Grim Fandago on the thing, but that is asking too much. Who knows, maybe someday someone will make a LUAvm and port it to the DS.

As far as the expense of homebrew, it is very inexpensive now. Barely more than it cost for a brand new DS game. You can get MircoSD cards very cheap off of amazon.com. I payed $11 plus a couple of bucks shipping for my 2gb microSD that I use in my DS.