It can be more than a little pricey to go with a complete disc brake conversion from the various suppliers however there are a lot cheaper alternatives.

The junk yard is not necessarily the best way to go. IF there is a bolt on replacement for your car (most do require a little tweaking) it is still not always the cheap way to go. Other than the spindles almost everything you drag home will need to be redone or replaced. While the spindles can be used the rotors will need to be resurfaced, calipers should be rebuilt, bearings and seals should be replaced along with the hoses. Additionally when ever you change major steering components such as spindles you should really have the front end realigned.

Generally when you buy the basic disc brake conversion kit from a supplier (around $200) you will also get a complete parts list of the rest of the parts needed.

Within the last 6 months I did a Disc brake conversions on my 57 Plymouth and a friends 63 Ford (Haven't done a Chevy lately but the cost will be about the same). The additional parts I need for the swaps included, new rotors, new bearings and seals, new steel brake lines, rebuilt calipers, small hardware kits, new rubber brake hoses and rebuilt master cylinder. By shopping around total cost for the parts (including core charges) was right at another $300 and in the case of the calipers and master cylinder I have a life time warranty that can be dealt with locally if needed. So basically for $500 I have the same thing that would have cost me $1000-1200 had I bought the vendors deluxe kit. Additionally I have new/rebuilt parts as opposed to used parts that have who knows how many miles/years on them.

And as Thunderbucket says, you will have to have wheels that are disc brake compatable.