I'd suggest putting one on before you get fish you care about. I was waiting on picking one I liked, and had put some clowns I hand picked after visiting a bunch of stores in my tank. Weeks later while I was still thinking it over, one clown went carpet surfing, which really sucked. Not just from the monetary loss, but more from having it happen to that fish I liked, and had invested time in finding and quarantining and ...
You can DIY your own kit on a simple rectangular aquarium like you have. Get some mesh net like
this from Amazon ($14). Get a frame kit like this
Ace hardware one ($15, certainly also available on amazon, buy a black one if you can). You'll need a saw (hacksaw) of some sort to cut the frame kit. It'll just sit on the lip of your aquarium frame. If you want to drive to Redwood City I might even have enough mesh you could have to fit (I'd have to check though).
Not as posh as the acrylic ones, but the frame will be slimmer and if you get black it'd probably look really nice on your tank. Also, it won't take 6+ weeks to arrive.
Here's my DIY lid for comparison.