A year ago I got a T-Mobile Prism II, a very cheap Android phone (made by Huawei) that cost me only $30 new. I don't think the phone is made anymore. T-Mobile now sells them directly as a "pre-owned" phone (whatever that means) for the same price directly on their website.
The Prism II is slow at times but I've found it very usable. (It's only a 3G phone as well.) I use it as a day to day phone. Then again, I'm not a power user when it comes to phones, so having a phone that can handle lots of apps etc. isn't important to me. If all you need is a "travel phone" it should work well for that. I had T-Mobile unlock it (had to use it for a couple of weeks first with my regular plan) and then could have bought my own SIM in Europe, but I didn't need to - I only needed T-Mobile roaming.
I've been a T-Mobile monthly customers for years. Even though the Prism II is a "prepaid phone," I've never used it that way, and once I put in my old T-Mobile SIM card I would never have known it was a prepaid phone at all - looks just like any other Android phone.
I used it in April in Germany with T-Mobile's "Simple Choice" plan and it worked quite well. Got only 2G data most places - slow but usable. The phone also supports WiFi calling, which means FREE phone calls to/from the US from Germany while you are connected to a good WiFI signal. Otherwise, it is 20 cents a minute calling back to the US or within the country you are in, if that country is part of T-Mobile's international roaming. Not all countries are on the list; check T-Mobile's list before you travel somewhere to make sure roaming is supported.