Back when I was on 992, we would just drive the parts down to the local FedEx office, where they were more than happy to help us with our unusual request (they only asked that we come after 7pm, when they aren't as busy).
If you want to buy a scale, I would recommend a scale with a wired remote. This will allow you to place a plywood platform over the top (you could even make up a nice wooden cover that fit the size of the scale if you wanted), and still be able to read the numbers.
The price of such a scale really depends on the accuracy you are looking for. Costco has a
Digital Shipping Scale with wired remote for $50 that is good to 310 pounds, but the accuracy is (+/-1.0% + .22 lb), which translates to +1.52/-1.08 pounds for a 130 pound robot.
For a more accurace scale, such as this
Health-O-Meter H349KL, which is accurate to ±.2%, or ±.26lbs @ 130 pounds, you will need to spend around $250.