I don't mean to sound rude or insulting, but your post is very difficult to read. So please let me know if I misunderstand something you said, I will try and answer to the best of my knowledge.
The ABS pump you are referring to is called the Hydraboost unit, it consists of the ABS Module, ABS Solenoid Pack, Acumulator Tank, Acumulator Pump, and Master Cylinder assembly. The unit is an all in one package and the Toyota Factory Support says to replace the entire unit if something internal is faulty. So you will not be able to get the Dealership to do anything other than replace the entire unit. $2600 for the unit sounds about right for the dealer price, its similar to what our dealership billed the warranty company when we replaced my Hydraboost unit because of failure.
You can get the entire assembly from
Toyota Wholesale Parts - Authentic OEM Toyota Parts direct from Village Toyota Parts | Village Toyota Parts for about $1800 + Shipping & Tax. Its still an expensive unit to replace entirely, you can buy parts individually for the unit, but there is no factory approved method of diagnosing a failed unit other than process of elimination. I tried to figure out ways to diagnose a unit myself (I still have my old Hydraboost unit torn apart, wrote it up in this thread;
http://www.toyota-4runner.org/4th-gen-t4rs/120125-hydraboost-brake-assembly.html) but you will not be able to do so without at least a factory scantool to diagnose the ABS and Acumulator components.
Could you please describe your problem further? What do you mean the brakes push back, does the pedal become very firm, or does the pedal actually force itself back up against downward pressure? I haven't come accross a vehicle that exhibits this type of symptom yet. I assume that if the dealership has diagnosed it as the Hydraboost unit, they've checked for siezed calipers (common along the colder/rustier areas) and other brake related issues.
I'm sorry I can't be of much more help at the moment.
