There is a lot of differences between the gnerations. LB&/LLY are closer together then say LLY/LB7 to the LBZ/LMM's but in no way could any transplant/engine swap be considered cheap hp.
Between different ECM's, some bellhousings, tranny cooler lines, 5 (lb7/lly) and 6 (lbz/lmm) speed ally's, different injectors, wiring harnesses and a load of other things im forgetting to mention. It would be an expensive swap unless you had an entire doner and wanted to make the retrofit work.
IMO the different stock generations to me are different levels of strength and durability. "Cheap" HP is easy to find in any duramax, making it reliable is expensive.
2004.5 2500HD LLY/Allison Crew Cab 4WD Black on Black - Leveled with Bilsten Shocks - EGR Blocker Plate and resonator delete - Roll and Lock Bed with a 60 Gal. custom auxilary tank - Cognito Idler and Pitman Steering Braces - Jotto Laptop Mount - MBRP SS 4" Turbo back exhaust - SD Stainless Steel Tie Rod Sleeves - All on Headlight Mod - Quick release Oil drain valve - EFI Live
V2 with DSP5 from SoCalDiesel - PCV Reroute - 3 Gauge A-Pillar with Pyro, Boost and Aux Fuel - LBZ Air Intake MP - 10 and 2 micron in line fuel filters - KD Lift Pump - KD Pump Rub Fix -