To answer the original questions;
Yes, you can just buy a lock and barrel and they will swap/drop in
Like Lonewolf said there may be a bit of fitting too the lock plate and in my experiance there may be a bit of adjustment needed at the wedge pin/lug for a snug fit. Both easy to do at the kitchen table.
Cost effective? That's a roll of the dice. You'll hafta keep an eye out for the parts you need (lock & barrel) at the price you want to spend.
I have seen Renegade stocks go on ebay as little as 60 and as high as 200, it's really a seasonable issue. Folks with the parts you want usually know what they'er worth.
If you find another perc barrel you can get an aftermarket breech plug for about 30 and re-breech the barrel to a flint plug, but that takes some know how and filling/fitting/drilling.
My 2 cents,,,