Glenn, I've bought three mando's in my life, all of them cheap.
The best one cost around $300 new. We were playing in a church one night, and my son, who was switching between the guitar and the mando, shifted his chair and we heard a loud CRUNCH. He had stuck a chair leg through the top of my mandolin. When he picked the chair up, the mando was stuck on the leg. The congregation thought it was hilarious and part of the show, and we kinda went along like it was. It broke his heart, but I was able to piece the wreckage back together, and it's barely noticeable now. He loved the instrument, and I gave it to him after I got it looking good again.
Mando #2 is a Martin backpacker. It cost about $200, and I foolishly bought it because it was the only instrument in tune out of all of the mando's in Allen's Music Shop in Paducah. The backpacker really doesn't have a good mellow sound, but it's tough and I can leave it in a hot car without worrying about it coming unglued. And it stays in tune.
Mando #3 cost $100 brand new. I bought it for my granddaughter a few years ago, and I honestly believe it sounds better than the other two.
I fooled with a nice Weber mandolin all afternoon one day. The music store was selling it for a friend for $500, and it was worth every penny, but ol' skinflint me was hesitant to drop that much money on yet another musical instrument. By the time I had driven the 30 miles home I had decided to buy it, but when I called them, it was sold. . .
I'd like to warn you - instruments are like tractors. You always need just one more. A musician and his money are soon parted.
Zach is right - the $50 mandolin would probably get you started.