Well, you could do the M3 Lite, seeing as how it does have everything you need.
But, older GBA solutions do the same thing, and you have an R4 already, you don't need DS features, and you don't need to spend the money.
BUT.
Older GBA solution were one-game-at-a-time systems.
Not this "Put as many as you can fit on an SD card" sort of thing like our DS Slot-1 cards now.
If you have money, go ahead and get the M3 lite.
The G6 Lite is a good alternative, and may be cheaper in some places.
EZ Flash IV will also do what you need it to do, and is my personal recommendation in this particular case. (NOT the lite version, the original EZ Flash IV)
You can find it
herefor about as cheap as it'll get.
So, simple as that.
If you want GBA support with cheats, get the EZ Flash IV, or the M3/G6 Lite.
If you don't care about GBA Cheat support, get yourself the EZ Flash 3-in-1 expansion, for about $10 less than the EZ Flash IV.