I started with a Titan F6 singly ply, and I love it. It's about $100.
There is a drawing on the Titan website that shows you were to measure, I think. What I was told to do - and I did - was take my chest and arm measurement, call Titan and ask what size shirt they recommend, and then order my shirt two sizes smaller than what they recommend. 
I have heard that Inzer makes cheaper beginner bench shirts, like around $60 that are not as good but easier to get into and out of than the Titan ones, and they may be easier to learn from, especially if you are a beginner and trying to do it yourself.
If you have a proper fitting F6, you will never be able to get it on/off by yourself.
It depends on what you get. I started out in an inzer HPHD Blast shirt. I really didn't like it because I felt like it was pulling the weight over my head (i'm a natural belly bencher). I then switched to an Inzer single ply denim. This shirt was fine, once I figured it out, but I felt like I wasn't getting much from it other than seam burns. I then went to an Inzer Radical Denim, which also seemed to just fall short for my liking. They all cost less than $100 and I think any of them might be a reasonable beginner shirt to learn how to use a bench shirt. The HPHD required 2 people to get me into. The denims I could get on with only a little help, but getting out of them was a real task.
I started using a single ply Rage X last year, which I think is probably the best shirt I've tried out to date. It gives great support, isn't ridiculous to get into, and seems to be wearing well.
My wife on the other hand has had more problems with bench shirts than any person I know. She's tried a EPHD Blast, multiple Rages, a Rage X, and denim. She has problems with all of them. I'm debating just seeing about her switching to an F6, but I'm almost afraid she won't like that one either.
