Mines on about 110k, and nothing's been done to that either, some of the problems seem to stem from corroded height sensors etc or the mounting brackets so i keep them and the pump and everything else visible well sprayed in ACF50.
Airbags themselves as seen on some really good videos online (i've done a post linking one or two if i recall), mainly in the US and not necessarily on Prados because other large Toyota/Lexus models are fitted with the same system, are really quite easy to change, easier than a spring.
If i get an airbag failure then i'll just slip two new ones in, probaly genuines as they've lasted so long, if it's more involved and likely to cost £hundreds then i'd be tempted to fit a conventional spring conversion kit, but won't do it out of choice because the handling and comfort of airbag sprung Prados and others is so good i would want to keep it like that for as long as possible.
Also sometimes lowering the back end makes it just that bit easier for one of our dogs, 8 year old female cocker, to jump in the back...note if you placed a lamp chop at the top of a 6 ft brick wall i can assure you she'd manage to get it somehow but we're all soft about our dogs.
I have no idea how much a new airpump or sensors would cost nor if there are viable aftermarket alternatives.