'Game Mechanics Design' is for looking at aspects of game play from a more conceptual level. "How do I...?" questions (implementation) go to the Support forum for the engine you are using.
I've moved this thread to RPGMaker MV. Please be sure to post your threads in the correct forum next time. Thank you.
Have a Common Event, with parallel process.
Select a new variable switch (and name it so that you don't accidentally use it for something else as well)
Select Game Data (near the bottom) and click on the ... at the end.
On the new tab select Other and then Gold from the drop down menu.
Click OK
[That variable switch now keeps track of how much gold the party has.]
I assume you only want this to run once, so you need a way to ensure that.
Conditional Branch
Create a new Switch and name it e.g. Gold Award
Choose OFF (because this is what you want to happen if the award has not been given).
Next line, new Conditional Branch (i.e. it is inside the first Conditional)
Select Variable and choose the variable switch you just set up
Select the drop down box (shows 'Equal to'[ by default) and choose 'Greater than or equal to' from the drop down menu.
Type in the amount you want in the 'Constant' box
The conditional now checks how much money the party has by looking at the variable.
Next line put the command to give the award.
Turn the Gold Award switch ON so that the award is not given a second time.
Leave the 'Else' sections blank because you don't want anything to happen if the gold is less than the amount.
Alternatively, when you create these conditionals, uncheck the 'Set handling conditions...' box, as you don't need an Else for these.
This is basic eventing. I strongly recommend that you look at Andar's
compilation of info. In particular, he gives a link to a playable tutorial for the Event Menu Command which teaches what all the various possibilities are and how to use them.