I wouldn’t worry about wets for a while, most club day events usually have a "Gentleman’s Agreement’ to not use them. Bigger meetings are different of course, but they are only something I have bought if the forecast for an event is bad. Otherwise they just sit in your shed and get hard.
I used to own a Prado, if the rear seats are folded down and forward you should be able to fit it in, perhaps the nose cone would have to come off but i think it may be wide enough to not have to do anything else. Rough guide to store a kart with all the fairings on you need a minimum of 2100mm x 1400mm
You should be able to pick up a KA100 complete for $2200 and a chassis that is a few seasons old for around $1500. (it wont look flash but it will get you on track) There are some good deals out there, sometimes club members are willing to sell things for a bit less to get bums in seats so it might be worth talking to your local clubs members. They should know whats around locally.
I’m also from the Country, numbers can be a bit low at times but if there are 3-4 evenly matched guys in the same class it can still be fun. I race away 4-6 times a year at open meetings, when it doesn’t clash with life, and most fields then are in the 10 -20 region.
Fuel used at most meetings is what ever the local servo has in the 98 octane variety (Caltex’s vortex 98, BP’s Ultimate 98) there are some “Race fuels” that are used and that are legal according to Karting Australia, but I haven’t seen them used outside of the national series.
Download a copy of the rule book and have a read there is a lot in there, about fuels and other things, but it is worth wading through.
$1.60/L of fuel and Kart 2 stroke oil is around $30-$40 per 1L pack
Bank on using about 1 liter of fuel mix per race.
KA100 Fuel mixture is 20:1 or 50ml of oil per 1 liter of fuel. You could use either more or less oil but 20:1 is safe at the recommended Carby settings
Not sure about restricted 125 mixtures.
Race day fees at my club are $30 per entry, and prices would range up from there.