The kits are pricey and are designed for non-ac cars. If your car was an original ac car you might consider upgrading all the underhood components like I did. I bought the VintageAir universal hose kit that included all the hoses, fittings, and dryer for ther system. It alone was about $100. After discussing with several AC experts, they all agreed that you want as big a condensor as you can fit up front. I found a new 26" TruFlow condensor that matched the radiator opening nicely for $50. I went thru everything including the inside AC air box and replaced the factory vacuum controller with a NOS unit.
Am impressed by the difference in the systems. Finished up,the R134 cools great. It only held 2 cans and when it kicks on, you can hardly tell that its running.
Aside from my labor and the cost of chroming my custom pump brackets and machining my dual groove billet pulleys, I think it can be done for under $500.