New, $110k and up. Used? Depends. The overall value of a vehicle will depend on the make, model, options, overall condition, mileage, and engine hours. In 2005, the full size CH/CL/CV trucks were good trucks... the Granite series which replaced the R-model in production, not so much. If you're looking at a Granite, might want to reconsider.
A Mack Granite dump truck can be purchased at the Macktrucks website. If this question is referring to the toy version it can be found as well at Amazon, and eBay.
Between 20,000 and 30,000, depending on specifics (model, type of dump body, etc)
Many cities have an authorized Mack Truck Dealership. They offer new and used Mack trucks for sale or can help you locate the model you want. If your city or surrounding area does not have a Mack Truck Dealer, you can also look in your local newspaper classified ads under "Used Heavy Equipment" for Mack Trucks.
Special tow trucks are called in to haul larger vehicles.
I have not heard of any common electrical problems, you can check with Mack trucks for technical service bulletins on your specific model.
Depends on model, configuration, and options.
What model and configuration? You could be talking about anything from a single axle to a centipede or superdump. Typical GAWR for a tandem truck is 50,000 - 54,000 lbs... it depends on wheelbase, type of road it's on, bridge law formula, etc.
About 6million dongs or $150,000 US on average
No such model for that year. The RD series (and you're probably thinking RD688 or RD690 - there never was an RD6) was discontinued at the end of the 90s, and replaced by the CV series Mack Granite.
Depends on what model engine it has. Can't answer without knowing this. Big difference between, say, and EM6 and an E9.
22,000 - 25,000 lbs or so.
At a Mack Trucks dealership.