I think the cost is high. That said, I also thinks it’s justified.
All I can say is get involved on a club’s executive, and you’ll quickly see that the costs charged to the competitors are not all that out of line with where they should/need to be to keep the clubs running. And the costs for some clubs are higher than others for a reason too.
One thing that allows club events to be cheaper for the entrants is that they are generally run predominantly on a volunteer basis. While most clubs are fortunate to have these volunteers who rarely get the thanks they deserve, as the saying goes, you do get what you pay for.
At a National event, you want quality and consistency out of your officials – race director, tech personnel, all the way down to registration, etc. This means to keep the same crew, you are flying people around the country, putting them up in hotels, feeding them, and paying them for their time. It’s also only fair to the host club or track-owner that they get something for shutting down their facility to regular use. Some bigger events will beef up the amount of paid medical personnel on site. Etc… more costs to hold the event, meaning higher entry fees.
Karting just doesn’t bring in outside sponsorship money at the same level as other sports, which means that a higher portion of the costs have to be paid by the entrants.