We don’t work with nylon, so we couldn’t give you a decent answer. I’m told that Wal-Mart sells nylon and cotton ropes at very reasonable prices. I would also try Ace Hardware. If you’re venturing outside of Baltimore, Harbor Freight has a wide selection of rope, including glow in the dark/UV reactant rope.
Another good bet is to head to LF&P when it comes to DC. I know a ton of rope vendors go and have awesome rope, but it tends to be expensive.
Hope that helps.