How expensive......
Welcome to the site. Take some time and cruise through the Projects section.
One poor guy in there has been building his for over 2 years. It has cost him a lot of money, and he hates to admit that part. I heard he even took a second job to help finish his truck.
Some others have swapped there motors pretty cheap and in a much shorter time frame.
My guess is ......Well it depends on you and how much work or experiance you will put into it.
Good luck!
Rob ( The 2 year builder )