Some of the cheapest flights to Vietnam are on AirAsia and VietJet Airlines. You can book online (using their websites) and get a good fare if you book in advance. You could also book an AirAsia flight to Yangon, Myanmar, for about 30USD, then just never use the ticket.
If you can't get an account at one bank, walk out and go to another bank or another branch. Eventually, you'll find one that gives you what you want with a simple visa in your passport.
Report back after you get your visa and let us know if the police visited. There are lots of conflicting stories about them visiting or not, so it's always good to hear concrete details. Good luck!
If you want to extend your visa, the immigration officer will want to see a receipt of your TM30 filing...so the answer is Yes. The landlord is responsible for filing this and should be fined if they don't. However, in reality, if you go to Immigration to extend your visa and don't have your TM30 receipt, you will likely be told to go to another window and file your own TM30 form, then come back with the receipt to process your visa extension. In this case, you will be the one paying the 800thb fine. Note that you can self-file this form with Chaeng Wattana, and you can find detailed instructions if you search this group.
For any reason, a Thai Immigration Officer can ask any foreigner to show proof that you can afford to stay here, and that means 20,000 thb or the equivalent in any currency. Cash. If they ask and you don't show the money, they can refuse you entry at their discretion. Easy as that.