I took a pair of 1 day kart racing classes from Jim Hall's school in Ventura/Oxnard. It is possible to see the track lay outs on google maps, Ventura Fairgrounds is where most of their lessons are. The other in Oxnard is at 2600 Challenger Pl, Oxnard, CA 93030. The track runs counter clock wise and from turn 1 to turn 4 I would just barely pass 41mph which feels plenty fast with your butt just off the pavement. Cornering g's were in the 1.2-1.5 range i am guessing. Was enough that after day 2 and pushing against people with racing experience my ribs were sore from a not so well fit seat.
The 100cc karts could get my 260 pound fat ass up to 41mph at the end of a straight and could whip into corners pretty damn well. I still want to buy a 125cc kart for fun, have some tracks local to me. But it is way down on my list. I know my speeds because I was using a gps telemetry software while video recording my runs on the track. A shifter kart would be fun but not at added expense.
Used and somewhat abused serviceable karts are in the 2500-3500 range in my area. If you are a bigger guy then CRG chassis are likely way to go as they are more rugged I guess than the ultra competitive lighter weight racing frames.
For a fun toy, 2000-3000 is my ball park and I realky want to buy 2 so my dad and I can have some fun for a dew more years before hit hits the big 70. Yup, he was 64 and taking the kart class with me. 2nd class he hurt himself weeks earlier and could only do half of the 2nd day class.
Also look at TAG karts. I say it only because the starter option seems nice. I dont want a race spec kart. I want a fun track day toy that doesnt need 2 people to operate/start.