Terry is being too polite. Let me put a finer point on it: it is a near certainty that your plumber, or whomever told you that, is ripping you off.
It's that simple.
Unless you installed a $4000 Toto Neorest toilet or a $1000 Toto with the tank in the wall, the "guts" of that toilet consist of a fill valve available at Home Depot for $10.47 and a flush valve that costs about $25. Fill Valve. Flush Valve. That's all that's in the tank. The links to the products are below.
http://www.homedepot.com/p/Korky-QuietFill-MaxPERFORMANCE-Fill-Valve-528MCM/203145423
http://www.korky.com/?p=Product&i=1161
The Korky products above are approved and perfect fits for Toto. Korky makes the Toto-branded Toto Universal Replacement Fill Valve, which costs maybe another $10, and is identical to the one I linked to above. (Some Toto toilets now also use a piston-style flush valve, which should be available for about $35.)
However, most of the flush valves never ever need to be replaced. It is a very rare instance that they do, only when something breaks off of them, usually from mishandling.
Otherwise, all one needs to change is the seal, usually in the style of a flapper. The universal Toto flapper is also available at Home Depot. It costs $14.
http://www.homedepot.com/p/Korky-3-in-Toilet-Tank-Flapper-for-TOTO-2023BP/205213624 Some other Korky flappers will fit your Toto, and they are even cheaper.
If you are able-bodied, replacing the flapper or the fill valve on virtually all Totos is a 10-minute DIY job. Replacing the flush valve is a bigger job, but I seriously doubt replacing the whole flush valve is necessary. That would be very unusual.
Plumbers can charge whatever they want, but if yours wants a lot of money for either of these replacements, you should feel free to use this forum to learn to do it yourself, or find someone else who will do it cheaper.
As to the seats, most Totos will take any standard seat, including inexpensive ones from Bemis or Mayfair, which you can buy online or at any decent hardware store or Home Depot. The Toto SS114 is nice, and it is available through lots of sales channels.
Oh, and if someone told you the fill valve was "leaking" because water was dripping off of it, they are a liar. That's normal. If you mean the toilet was "leaking" because it was running, then usually all that is necessary is to replace the $15 flapper.
Tell us what model Toto you have, and we can give you a more definitive answer.