I went through the same thought process... Started out with the mesh rod sleeves that are sold at the sporting goods stores. They work great but can be pricy. I remove the baits/lures when I'm done for the day... but leave the SNAP tied to the line. The SNAPS were always getting entangled in the mesh.
Went to a cloth/ripstop material rod covers (from eBay). They worked better (for me) because of the SNAP issue... but still run $3.50-5.50 each.
I'm always looking for a better (and CHEAPER) alternative, and came up with something similar to the pool-floatie tubes: the foam "pipe wrap" you can get at the "Big Box" home-repair stores!
I forget the inside diameter that I found works best... 5/8"? Maybe 7/8"? It's not as big OUTSIDE as the pool-floats, but works well on my baitcasting rods. The 6' length easily protects rods up to 7' long. The inside diameter fits snuggly on the top "fore-grip" to hold it in place.
They make a split tube and a solid tube... I use the solid tube and they're only like $0.98!! And you also get your choice of colors (as long as it's gray). <g>
They probably still aren't the best for a rod-locker (too bulky), but work great for the commute in an open boat, car, trunk, or pickup bed!
I use them on all my baitcasting setups, but still have to use the mesh or cloth rod covers for my spinning setups because of the bigger eyes.