A lot of companies have "Stages" of upgrades. Usually each stage can be sequentially achieved by adding additional components to the previous stage, or you can just start at a higher "stage" by spending more money initially. There's no standard for what each "stage" entails, it's on a tuner by tuner basis.
EDIT: For example:
Stage 1: Exhaust manifold, wastegate, BOV, turbo, downpipe, cats, intake, fuel pump, engine management
Stage 2: Add head gasket, boost controller, FMIC, larger fuel injectors
Stage 3: Enlarged turbo, larger injectors
You can start at any stage, just have to spend more money.