OK I thought he was looking at a visa in country to solve his issue. Good that there is an option that does not require 400k in the bank :). Vientiane is usually the easiest for most types of visas with minimal paperwork. If he was worried he could go to a visa agent and get them to sort out the easiest option for him perhaps.
From Australia, Yep. Be a crappy way to start your holiday if they made an issue of it. But then I have flown from many other places into Thailand and never been asked. Just book a cheap onward or 'rent' as someone suggested in the comments.
Be a crappy way to start a holiday though. Most times people get away with it at entry into Thailand once they get past the airline check in. Most likely to have problem with airline and not in Thailand.
Doesn't matter if the ticket out is with another airline or destination as long as it is a ticket out. The airline can check you have a ticket out before boarding and so can immigration at the airport on arrival. A return ticket is not necessarily required, onwards ticket is fine.