Second-hand mics are a good way to go; you can typically buy a newer model mic for just about half of what it would retail for. (I say "newer model" because a true vintage mic like a U47 in good-to-perfect condition will often be 3-4 times the price of a new reissue, maybe even more.)
My only advice when buying a used mic is to ask the seller some specific questions to get a feel of his practices and habits regarding his care of the mic and his gear in general. I made the mistake of skipping such questions a few years back when purchasing a used Shure KSM42. I met the seller at a gas station halfway between his place and mine and checked out the mic; it looked perfect: no dings or scratches or anything even remotely noticeable. The pattern switch felt perfect when I moved it, and the XLR output pins were not corroded or damaged in any way.
I bought the mic, took it home, and started tracking with it. I was already familiar with the sound of the mic, having used it previously in various studios, and there was definitely something missing, specifically in the high-end frequencies. It was really dull.
So, I contacted the seller and explained the situation. He said he couldn't understand why that would be, but he admitted he hadn't actually used the mic for nearly a year before selling it to me.
I took it to my tech wizard (if yer just starting out in the recording field, finding a nearby, reliable tech wizard is KEY; befriending him is also a VERY good idea) and explained the problem. I left it with him, and he called a few days later to tell me he'd found the problem: the mic capsule was almost entirely covered in dust.
So I called the seller again and told him what my tech found. He was very surprised; I quickly found out he was surprised because he was pretty much clueless regarding the proper use, care, and maintenance of microphones. When he told me previously that he hadn't used the mic in nearly a year, I assumed it had been properly stored in its protective red velvet cover, which is what the mic was in when he brought it to the gas station to sell it to me. NOPE. He had just left it mounted to a stand in the corner of his studio, where it sat and collected dust for a year.
I have been recording since I was 12 (over 20 years!) and have studied the craft both in college and on the job. I've worked in many different studios in various capacities and have had the fortune to work with some great producers and engineers (John Agnello, Mike McCarthy, I even took a master mixing class from Eddie Kramer while I studied at Berklee). Granted, they all have different ways of doing it, but ALL of them were Nazis about their mics. McCarthy covered nearly every mic with a plastic sandwich bag overnight (in a situation where the mics couldn't be moved, like when they've been setup and dialed in on a drum kit and there are many days of basic tracking) and would even do this when they wouldn't be used for even just an hour. That's how concerned he was about dust and other particles infesting his capsules.
So yeah, long story short, second-hand mics are pretty much the way to go, but MAKE SURE the seller is up to snuff when it comes to the proper use, care, and maintenance of his gear.