I agree with DarkMaster that there doesn't seem to be any cheats for this game (endemic of many other JRPGs I've played - I guess they consider it beneath themselves). However, games of this type 'compensate' for that by being completely defenceless against casual ram hacking. So yeah... if you want to cheat, there's no other option but to roll up your sleeves and go in with Cheat Engine or ArtMoney (whichever you prefer).
Now if all you want is cash, that is of course utterly trivial to change.
HP and experience are unusually interesting/annoying. From what I can tell, the game assigns RAM values to battle values (HP, XP, essence) at the start of every battle. Once the battle is over, it wipes those addresses. I presume this is because it was designed to run on systems not overflowing with RAM so every little bit it can recover helps.
Anyway, the knock-on effect is that every time there's a battle you have to find the addresses all over again, and once you get more than three characters, unless you cheese XP (in which case, why bother with Cheat Engine?) you're going to clear the stage long before you find all the addresses. For this reason, I recommend you only bother on the early battles, where it's handy to 'powerlevel' your way through and make the early game a little less tedious. Beyond that, you'll probably manage just fine, occassionally intervening in the 1-on-1 duels, where giving yourself free heals makes the whole experience much less miserable.
If you do plan on mucking around, here's what I've observed:
HP is recorded in two distinct addresses. Changing one but not the other makes the game very unhappy and doesn't affect your actual HP. However, if you change both then the game doesn't notice something's wrong and all is well. You can use this to heal your characters in a pinch.
For XP on the other hand, you probably aren't going to know the exact value at a given point, so naturally you've got a bit of extra work narrowing down an unknown value. However, if you're diligent, you can probably get it in about three or four turns. You will, however, note that it doesn't narrow down from eight addresses, which should be duplicate sets of four - three large numbers and one number between 0 and 100. This is the number you want. I've tried modifying the other three, but either nothing (noticeable) happens or the game crashes. Naturally, you need to modify both XP values for the number to change. I don't recommend altering the value outside its natural range, though, because weird things sometimes happen.
If you're wondering about THAT mission too, I couldn't get Cheat Engine to find the timer value. However, it's quite possible that it exists as a float; regrettably it didn't occur to me to try that out then (I only looked for integers) and I don't plan on revisiting that mission any time soon. Although if anyone wants to have a go, I'd be most interested to hear the results.