So ya wanna bus to play with??
The most important decision in choosing a bus is.... how much money do ya want to spend. Not only on the bus but the whole conversion process.
Gas buses are cheaper than diesel buses. Diesel last longer. Resale is better for diesel. After spending lots of money, time, and thots, most money spent will not be recovered. This hobby is expensive but hugely rewarding in many ways. The act and money spent on a bus camper is actually cheaper than most money absorbing hobbies. You can make a bus your way and camp anywhere reguardless of completeness. Bus camping is the best fun.
If ya buy a cheap bus, who can say, what is low or high value. My bus is a king of buses, the famous Crown bus.
Become a patron of Ebay and keep a history of sold buses of all types. Average Crown bus is going up now about $2600 depending on certain factors. Usually the more ya pay, the more bus ya get. Frank