I paid a ticket to KL 2200 return, it took me an hour to flight there and I didn't have to deal with all those stupid people driving on the street. If you have lived in thailand you surely know how dangerous are those minibus which are often driven by drivers who are fxxked up on drugs/alcohol.
you can apply for a tourist visa (60gg+30gg extension @1900baht) then you can go to a thai embassy in a nearby country (KL? Laos?) and ask for another tourist visa (60+30gg again). That will give u 6months which seem to be just what u need. There's no need to switch passport, there aren't problem at all when you stay here for 6 months.
You better get a visa, you've already got here for 150days and done border bounce twice. Even if you fly out and in, you might not be allowed to get in the country or get a lot of questions about the purpose to be in thailand which is clearly not just for tourism..
there's a post on another thai visa group of a lady from Zimbabwe who bought a ticket before getting her visa (having a ticket is required). The visa was denied and it seems she bought a non refundable ticket which she has probably lost. This folk appears to be smarter so he will probably apply for his visa using the onward ticket as a proof. In the worst case his loss would be just 20bucks