Hi, Jason! It seems like to me, you're basically trying to get the player to bid a certain amount for an event, right? Here is what you'll want to do.
In the event editor, you're going to use the command 'Input Number' which can be found directly under the show choices command.
It's going to ask you to select a variable to attach the number to; in your case, go ahead and pick 19.
Select the amount of digits you'd like the player to be able to input; the highest you can go is 8. (So they'd be able to bid no more than 99999999 gold, for example.)
Directly underneath that, click on 'Control Variables'. Pick 19 in the 'single' section at the very top; then, under 'Opperation', click 'Set'.
Beneath that, in Operand, click 'variable' and pick 19 again.
What you've just done is allow the player to control variable 19; whatever number they input, will be what 19 becomes. :)
After that, event as you normally would via conditional branches and such! I hope this helps, and if not, I'll post some screen shots for you. Good luck!