How much powder do put in a 44cal black powder REVOLVER?
Typically, 20-30 grains. Depends on the bullet/ ball you are using. Contact the maker, get a copy of the owner's manual, follow instructions.
Black powder is much weaker than smokeless powder. Smokeless powder, for this reason, once invented(much after black powder), replaced black powder in guns. However, black powder is still used in fireworks because the extreme explosive power of smokeless powder would prove too dangerous in fireworks.
To even begin to give an accurate value I would need to know the condition, maker and model. If you don't know these you can compare yours to ones in the on line auctions, like gunbroker and auction arms. Look up black powder pistol or black powder revolver and compare photos to what you have, that should help identify and give you a value as well.