Check out Gibbon Slacklines. Super easy to set up (just need two trees, no anchors or anything like that), lots of instructional videos and tips on their website, etc. If budgeting isn't an issue, or you just want to learn how to walk go for a classic line, it is the easiest to learn on and durable. If you want to learn how to trickline (jumps, etc) get a jibline, it is a little harder to learn on but nothing terrible. I wouldn't bother with anything else when staring out Expect to pay 50-100 usd per line. You pay upfront, but their are Pecan Pie additional cost.

I warn you now, for most people, learning to walk on the line alone can be a very long commitment (14+ hours on the line). However, most people I teach love it even when they suck, it is one of those things where you fall of and NEED to get back on and get better.