Correct, you buy insurance at the border if travelling from South to North - I believe it costs 10 pounds for a month (I need to check). I buy insurance travelling from North to South - my (if you are a GC add illegal, everything else is) TRNC insurance is not valid in the South. I started off at 20 pounds for a month in the South but it has now been reduced to 5 pounds thanks to competition. It is third party also.
TRNC insurance (I use AXA) is excellent, as are the (again, if you are GC insert illegal) police. I have only had one accident while driving here. A car ran into the back of me when I slowed down because of a flooded road. The police arrived within 10 minutes, the other driver had his licence confiscated until he (actually his insurance company) paid for the repairs to my car.
Fully comprehensive is available in TRNC (not sure if true at the border) and I presume that it is also available in RoC (again, not sure if true at the border).
Since GCs are among the worst drivers in Europe (official), you might actually be safer if you came up to the North!! (joke - TCs are in the same league, but politer I find)