The less expensive border/air bounce from Pattaya ?

From Pattaya best to use visa run agent to Cambodia.

Check out Maneerat Soi post office. 

I concur with the suggestion to use a border run company, though it can be pretty uncomfortable. Independent travel by public transport to the Ban Pakard crossing, negotiating the in/out yourself is possible, but not recommended except for seasoned travellers good at dodging scams.