First I would recommend hitting a couple music stores or pawn shops and playing a variety of instruments to find out what YOU like. If you are going to be happy with a beater mando - there's likely a bunch that you can grab for under $100.00.
For me - I was happy with my A-Style Kentucky. It didn't sound that good - but the action was really good. As a learning mando - it was great. Once you find a mando you like - do a search in classified's here - or ask for a particular make/model in classifieds. You'll find it.
Glad to see you picking up this fun instrument. Just realize - there is a very good chance you may not touch your guitar again!
"How many of you folks have seen that movie "O Brother, Where Ya At?"--Ralph Stanley
Turkey Creek #17
1958 Gibson A-40
2002 Martin D-28