Do yourself a favor and buy good used stuff & save yourself the agg of replacing that “decent used package” later. Been there , done that already and I’ve only been karting 2.5 years now. Yes it’ll be roughly $5500 – $6000 but I’m being honest. Spend a couple $$ upfront to save later.
Also, IMHO, don’t buy a Rotax, they are now a thing of the past in the USA and at this point who is supporting the Rotax?? Again, in the NJ area, go with an X30, by far the most popular motor in the area and real easy to get IAME parts. I’m not saying its the cheapest or most economical motor, but by far most common motor on karts in the NJ area.