There are plenty of mods already in existence for this sort of thing.
One, you can visit MATY for the money order mod that does that very thing.
Two, you can visit
Simwardrobe to get the checkbook mod that also does the same thing. Cllick on Sims 2 to the left, click on Objects and scroll down until you see Other Objects???. The checkbook mod is located on that page.
Or you can use the updated
Monique's Computer for BV that has banking features to give your Sim a loan, transfer money and so forth.
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