you won't have an issue. I just flew in from KL Malaysia on my 3rd 30 day stamp. Since late November last year this is my 9th month in the country. 2 60 day visas, 2 extensions, 2 land border runs and now re entry at don muang this last time. I was sure to be interrogated but the officer didn't even ask to see my exit flight. So you'll be more extremely unlucky to be denied than lucky to be let in. Enjoy your stay
Impossible too calculate so I can only give you my budget living in bang saray which is between 40-45k baht a month. But that's just living expenses such as rent, utilities, food, sundries, internet, bike fuel (own my own bike).
You could get the 6 month multi entry visa too. That would also work but for the time you're staying, may not be worth it be it I don't know how much it costs compared to the 1900 cost of extension
Unfortunately you have it back to front. The other way around a 60 day TR visa would have been cool with a 30 day exempt on your return for the 5 days. The way you're doing it you could either arrive visa exempt, move to your next country and apply for a 60TR there if you have the time or arrive visa exempt, visit your other destinations, return on visa exempt and apply for a extension at your nearest immigration office