Here is my budget weekend hack for a cheap Detailing Seat.
Find, (notice how I didn't say steal) a milk crate. You can find people giving them away in Facebook Market for example.
Turn it upside down and find a cheap cushion.
I got this one from Ikea, of all places for $10.00 as it is the right size.
Milk Crates are around 35cm2 and this one is 35x38cm.
https://www.ikea.com/au/en/p/malinda...lack-40326582/
I am happy to kick it around the Car as my drive is on a bit of a slope, but if you wanted it would not be hard to make a base with some board castor wheels, for another $10-$20