I have seen text radically retooled between RAM and ROM but most of the time it will be that compression was used so back searching the ROM with text you found in the RAM gets tricky. It might not be that and instead line breaks of placeholders ("you need ?? gold to buy that potion" sort of thing where whatever the game uses instead of ?? in the script is swapped out in favour of the current price).
If it is compression then the GBA has a standard compression option in the BIOS that most games use or use an equivalent of. There are compression logs and searching options, though I usually aim for something a bit more directed for text as most of those are aimed more at graphics.
Speaking of graphics if there are only 30 lines then the text (I am assuming menus and whatnot) might well be stored as graphics instead. Can check with a tile editor if you want.
If doing it properly as a big boy hacker then tracing is usually the order of the day. https://www.romhacking.net/documents/361/
is a nice guide, though rather than vba-sdl-h that it suggests we tend to point people at http://problemkaputt.de/gba.htm
these days as it is nice and graphical. If you know where it is in RAM you can set a break on write to that area just before it lands in RAM and for the GBA then whatever it is fishing out of the 08000000 through 08FFFFFF section (technically it goes to 09FFFFFF but unless the ROM is more than 16 megabytes then it will not be using that, and there others that are used even less commonly) a few instructions before is likely your text location, and also anything it changes along the way.