the following is applicable to most situations. If your car was being repossessed, none of it applies.
to answer your question, you need to answer a few more questions.
was this on private property or a public road?
when you first spoke to the tow operator, was the vehicle "hooked up" to the tow truck with hooked up being defined as such:
Hooked up means the vehicle is fully prepared for transport by attachment to a tow truck, lifted in tow position, with tow lights and safety chains attached and, if required, placed on a dolly in a raised position and the only thing remaining is for the tow operator to drive away.
per Texas law, if the car was not "hooked up" they had no legal right to tow the vehicle at all. If the vehicle was hooked up, they must allow you to pay a drop charge. For vehicles weighing less than 10k pounds (just about any car weighs less than 10k pounds), there is a maximum of $125 (which the operator had not exceeded so the amount was legit). If this was on private property, the pay to drop fee must be accepted as long as you stop them prior to them leaving the private property. If on a public road, you can pay to drop until they actually move the vehicle.
If he had clearly agreed to allow you to obtain the money from where ever you were going to get it, he had no right to tow your vehicle. I would demand a refund of (depending on whether it was hooked up or not) either anything over the drop charge or all of it. If they refuse, you might consider filing a small claims action as well as filing a complaint as sandyclaus suggested.