I dont think they charge way too much.
Try to take your car there but you can also call and inquire about the charges .
Oil is special and you need real genuine one no fake ones. brand doesn't matter as much as the type of CVT fluid does so you need to be extra careful and buy the right one
Lower chamber must be opened . First open the drain plug and let the old oil go out. Then remove the lower pan and jaali in it like a filter. Must clean all of that properly . Buy a new seal if available otherwise go for silicon while sealing the pan. Now locate the proper inlet for CVT fluid. Many people pour in from the dipstick hole and some through the bleed value
CVT is very complex so do your research first