Using artmoney both values are stored in int 4s. Sun is easy to find but you can only go up to 9990 i believe. Money was harder to find but basically because the lowest coin is 10 they store stuff one decimal point lower and multiply it by 10 for display ie it shows you have 10,000 but its stored as 1,000. Using that its also easy to find the money spot say you have 7850 search for 785 wait a few mins till you get another coin, say 7860 and refine to 786 presto inf money.
Yes, it is relatively easy enough to get it to work with ArtMoney (though as you said, the Money part was tricky). But to me, it's always a pain to have to redo everything every single level. Maybe I'm just doing it wrong, but I have to re-search on every level as it seems to change. Would be just much nicer/easier to have a trainer work its magic.
I guess the only things that would be nice that ArtMoney can't do is making the 'regen' time for plants, etc. to be instant or giving the ability to have infinite selection of items on the 'boss' levels... the ones where you can only use the items that come scrolling along at the top.