How much money can you get on Pokemon Diamond?

Answer 1

You can get up to 999999 poke.

I know some ways you can get a lot of money, though. if you go fishing in Canalave city with a super rod, you could catch a Staryu. it could be holding stardust, which you can sell to the cashier at the poke mart for a lot of money.

Also you can use action replay.

Or you can sell some fossils you find in the underground.

Or, if you go in to turn back cave which is in the spring path, south of Veilstone city. (you'll need hm rock climb!) if you get to the end of turn back cave, there will be a rare bone, which you can also sell or a lot of money. Also, if you find any rare candies, you could sell them (but.....why would you want to?).