Don't do what I did. I was looking online and found a CyberPowerPC prebuilt tower on sale at Best Buy for $450, and bought it the same day without doing any real research. It looked promising (AMD FX CPU, Radeon R7 graphics, 8 GB RAM), but turned out to be a lemon. That AMD processor is an FX-4300, which is severely underpowered compared to newer offerings from AMD and Intel. The AMD R7-240 graphics card can barely handle T:ANE (it struggles even on lowest settings), and because of that, I'm still using TS12 (which runs perfectly on max). It later turned out to be a refurbished four-year-old Windows 7 rig that was upgraded to Windows 10, something they didn't tell me. I've only had this PC for a few months and I'm already saving up for a new one. That could be kinda tough, seeing as how I'm just a bagboy at a grocery store... (also, I suspect the hard drive may be developing problems)
TL;DR: Don't go cheap. Save up. Research, research, research. And most importantly, DO NOT JUMP THE GUN. Take your time. You're not gonna lose your Trainz if you hold off for a few more months. If it sounds to good to be true, it is. Also, it doesn't hurt to build your own. It's cheaper and you could learn some skills that may help in the future, especially if you're looking at going into IT or PC servicing. There are guides online to help you.
Matt