the dstwo is like 35$, that is not a lot, considering an 8gb SD card costs almost 50$ already.
Also the price becomes worth it if you get painless gaming experience. I mainly bought all other cards i own for reference and personal experimentation purposes, my main card that runs EVERYTHING is the supercard. it may be 2 times the price of an Acekard2i, but it's worth it, that's what i am saying.
Take an iEdge for example, price around 19 - 21$, and it's a solid card. You still don't get all games to work on it, but the vast majority does. There is nothing wrong with this one.
The same can be said for other cards in the same price range, like the M3iZero, or the Acekard.
If you ask supercard users about the last time they had to use a patch to get a game running, then most will scratch their heads.
in my opinion, the 35 - 40$ for the card are justified.
But hey, maybe you can just get an R4DSN that is wood compatible. You will find that certain games will just not work, unless you can work black magic on your card. For updates of the card itself you need a DSLite or other pre 1.4 DS. That is one of the things i don't like about say acekards, R4's and so forth. Here, the Superkard and the M3Zero shine, because they don't need a console for the update. these are just some of the things to keep in mind when you want to buy a legit solid flashcard.
40$ to me is like the price of a single retail game i would have bought otherwise. It's money i gladly spend for such a usefull development tool
Oh and hey, with the SCDS2 you also got an (almmost) complete back catalog of GBA Titles. That is very much awesome, something no other budget card can cough up (yet).
But enough rambling before i start sounding like a sales rep or some shit.