The cost of a USPS money order at the post office depends on the amount the money order is for.
For money orders up to $500.00 the money order fee is $1.25 and for money orders above $500.00 and up to $1,000.00 is $1.70
The limit for USPS money orders is $1,000.00 each so if you need to make a payment of more than $1,000.00 you'll need to buy additional money orders.