I'm looking to create instant privacy by planting live oak trees. My question is whether or not the cost difference between a 65,100, or 200 gallon is worth going with the largest option? How long would it take for a 65 gallon tree to reach the size of a 100 gallon tree. or a 100 gallon to reach the size of the 200?

What are the costs of each of those sizes?

I'd go with the 65 gallon. I think the smaller trees will establish faster and be less susceptible to transplant shock.

I'm no expert and I'm just guessing based on having a bunch of oaks in this range over the years. I'd say the difference between the 65 gal and 100 gal is 4-6 years. The difference between the bigger two would be an even tougher guess... I'd say 12 years, maybe. Obviously there are a lot of variables, a big one being rainfall.

As the poster above mentioned, I'd be more concerned about the more mature trees not handing the transplant very well.

Unless there is a good chance you'll be selling soon, I'd go with the smaller tree, which will eventually catch up - link

go with the 65

What these guys said. The little ones will catch up due to the damaged root systems on the bigger ones.

65
But does it have to be live oaks?
There are other oaks that will grow faster and not be susceptible to oak wilt

You should be buying trees based on the caliper inch, not how much dirt they package with it.

I'd also recommend ball and burlap trees over container grown.