Does it need to be an L shaped screen?
I use a Bownet (I-screen with 7'X7' frame) & it works great. Set-up take down in a couple minutes, very light & portable. Not the most "heavy duty" net out there but it will stop any shot up middle (even a masher). Mine is going on 2 years of use & is still in pristine condition. Only drawback I have seen is that on really windy days you need to either stake it down (it comes with stakes) or put something heavy on the base to keep it from blowing over. This is because it uses composite poles for the net frame with metal base poles. Got mine out-the-door for <$150
People have also had lots o success with 1) Juggs lite & 2) pitchsafe screens. The Juggs is a bit more solid & costs about the same (maybe $20-$30 more ) but is not as compact. The pitchsafe is both durable & very compact but runs about $300.
You really can't go wrong with any of these options, just depends on what you want to spend
JJ