You can get 30 days without visa and 30 day extension after that.
A bus ticket would not work because of the boarder is not open between Thailand and cambodia by land. Get a cheap refundable ticket to malaysia or hong kong by plane.
To stay longer you can get a tourist visa which gives you 60+30 days or try with STV for 270 days.
You need to do it where you stay. Seems like 14 days is standard now myself and others in different locations have gotten the 14 day stamp. Might be because the end of covid extensions is near.