Honestly I got into the sport believing I could be cheap and affordable but it honestly depends on
What class do you plan on running? (Shifter, TaG, Yamaha, Briggs and Stratton, etc.)
What are your long term goals?
What level of racing do you plan on running? just club or nationals/regional events?
Tires are king, how fast do you want to go?
tires really depend on what class, shifters run super soft compound tires for maximum grip. most TAG classes run he Bridgestone YLC or MG Whites these are intermediate compound tires.
On the subject of new vs used, it really is about the level of racing, club or local racing usually you can be competitive with used chassis. If you buy used, for the love of god buy a one or two year old kart and inspect it bring a kart shop owner a long with you. New chassis the best on the market is probably the OTK signature karts (Tony karts, FA, Kosmic) The only problem with karts like these is the damage an inexperienced driver can do, smacking into a barrier or other kart could take a large portion of your Budget out of your pocket.