Are we talkin about a 99 K1500 or a 99 Silverado like the one in my avatar? Two completely different animals and it makes a HUGE difference in what axles you can or can't use and the price of the swap. Nobody makes a leaf spring kit for the 1/2 tons anymore that I know of. I got mine from Off Road Direct and shortly thereafter, they went belly up or sold out to someone else. There MAY be someone that makes a link/coilover kit still, but I'm not sure. Too much money for me.
Since my frame is only 37" wide where the rear springs hangers are for the front suspension, I had to use a 78-79 Ford Dana 60. They cost more. On an 88-98, you can use a Chevy axle, 78-79 Ford, or a newer Ford axle with the 36" spring width. I scored the front for 800 bucks in great shape. I regeared from 3.55 to 4.10, locked the front, rebuilt it, had to get lower adjustable kingpins to get the 2* of positive camber out, and got new Warn Premium lockout hubs. I also did some machine work to the hubs so a GM wheel would fit and I notched out the backs of the rotors for an ABS sensor so everything would still work.
For the rear I used an AAM 11.5 out of a 2500HD with an 8.1 gas motor. Already had 4.10s in it, good brakes and was ready to go. It bolts right in and uses the same spring width and parking brake cables. I sold the stock 8.6 rear axle for the same price I picked this monster up for.
An NP241 is your best bet with a Silverado. The K1500 already has one. My truck is a base model and has a floor shift transfer case, so everything was just as it was from the factory. I did a slip yoke eliminator and machined an NP205 1410 series yoke to fit and had a full 1410 rear shaft made.
Crossover steering came from WFO Concepts. Great prices, fast shipping, and amazing customer support. It's still spendy though. I got the front brake lines from them too.
Anyway, I had a very detailed parts list (with part numbers too!) on my last computer. Every part, piece, and miscellaneous expense was tracked. Anything from lug studs to the pigtail for the VSS. Last I saw on that, I was around 8000 bucks and I wasnt done. I've got about 10,000 in it, but I did it my way and built it how I wanted it the first time. You could do it a little cheaper, but it'll still be upwards of 6000 bucks. I already had tires and rims and some of the other parts, so that cut back on my costs as well as the stock parts that I sold. Again, keep in mind that this was a leaf spring setup. A buddy of mine did an 03 2500HD and the coil spring kit he got was about 2500-3000 if I remember right. My time was free and so was any machining work that I did. It really adds up fast.
