1) My first question is what will be the best(fitting engine) to swap into the z while not breaking the bank and around how much it'll cost.
K20 or K24. Both fit very well into the CR-Z engine bay and K-series is by far the easiest swap to do as its been done before and there are conversion components available, it is the most reliable swap to do and most adaptability in terms of replacement parts and further engine modification.
Price depends largely on whether a private individual is doing the work themselves or paying someone else or a shop to do it and whether new or used components are sourced and the one doing the sourcing's connections.
2) My second question is if it'd just be a better idea to buy a supercharger with performance headers, exhaust, intake and all or do the swap, with a reliable engine then add all those performance peices. Which one will give me more bang for my buck?
It is almost always easier to add forced induction to a factory installed engine, especially if it is a kit, than to do an entire custom power plant (engine) swap.