Since nobody so far has said they got refused entry, I would be surprised if you had any problems. Many years ago (10++), I went in and out once a month for almost two years, at least 19 times and they never said a thing except once. This was around the time when the immigration was first starting to get serious about visa runs overland as it was the normal way many people stayed and stayed and they wanted to change that. They changed 30 days to 15 days and made many announcements and you could read on thaivisa many reports of which border crossing was the most lenient that week and how/why people were being denied entry. But basically no comments at all about returning by air. This included a few trips to Singapore out on first flight back by 5pm. It was almost clear that the policy was officially to let people in at the airport and one reason may be that it is relatively easy to deny entry at a border crossing where a person can walk back where they came from, which is a country that has a Thai Embassy that could 'fix' the person's problem or at least give them a tourist visa. At the airport that becomes a hassle. And one last thing, you can offer a very honest reason which, in your case might be that you are waiting for the retirement money to be in the bank for 3 months...