Since the original question about cheaper alternatives doesn't seem to have been answered, the only one that comes to mind that is usually readily available is the EMS one, which has two pages where you can store a couple games, but it only has one save slot, so if you save a second game your original save is lost. They also require proprietary Windows software to add the games. I think someone made something so you could add games to the first page with *nix (including OS X), but that is a bit of a waste. I have a couple of these full of music software. They can be a headache.
There are other options, but I don't know if they will be cheaper when all is said and done. These are pure flash carts, and will require a way to flash them. I can think of a few people making them, plus you have some old ones, like the official "Nintendo Power", or whatever it was called, from Japan (this one is white, and the label has a place for you to write the games that are on it or something). Apeshit/ASM makes some carts and flashers, and everything I have ever purchased from him was great quality, so he gets a recommendation from me (he may not have a web shop right now, as he is changing some stuff with his business to focus more on gaming and less on chip music, and he is dropping product lines that others have started copying, which was mostly stuff for modding, like backlights, cases, buttons, etc., some of are now available from Rose Colored Gaming). There are also schematics available online to make your own.
I think the Smart Boy flash cart is made using those schematics, which were released specifically for non-commercial use. I may be wrong about that, but I am pretty sure they are in a legal grey area even more than most flash carts that people use for playing pirated games. I don't remember the price on them, as I was not interested after I found out about whatever it is. They are not always available.
Another kinda pricey option, designed mainly for the chip crowd, is the Drag and Derp, which you connect to a computer via USB. It will show up as a flash drive and you can easily add or remove stuff, but I don't think it has any sort of menu, so it is really only for one thing at a time. It will be particularly useful if you want to make backups of your saves.
A cheap option that probably won't fit your needs is something like
this. You will need some eproms and a way to flash them, so it may be more expensive in the long run, plus it is quite limited.
If you want more details on anything I mentioned, let me know. I think the Everdrive is the best bet for gaming, and I will probably eventually pick one up myself if I ever come across a game that is pointlessly expensive that I want to play (I am looking at you Pokemon, despite the fact that I got a copy of red for free, and probably have my original cart from back in the day somewhere).
Off-topic:
Which Pocket do you have? I never had one back when they were released, as I was still rocking my grey brick, then the translucent purple Color, and eventually the original silver GBA SP. When I got back into them I stuck with mostly the original ones, but I did pick up a couple more Colors for customizing, and an original GBA because it fit my hands better than the SP.
I had long wanted an Extreme Green N64 controller (still don't have one), and since it is an awesome color, and I didn't have a Pocket, I waited for a cheap one and finally added one to my collection a few years ago. They really do have much better LCDs than the bricks. I then swapped out my buttons for clear ones when I had to buy a replacement battery cover that it lacked.
I still carry it when I think I might get a chance to play games (mostly Metroid for this beauty), as the small size and great screen make it a winner for me, even if it is a bit small in the hands. As dorky as it is, I sometimes hold it and admire it.