If you don't mind using nylon most electrical suppliers carry 600' foot roles at a good price. If you know an electrician or a supply salesman you can buy it pretty cheap. I think I paid about $60.00 for 600' feet not to long ago.
I beleive the electrical rope is a poly and not nylon. The problem with the yellow poly is that it gets small stickers on it that sticks in your hand when pulling it up.
There is a place in galveston that is a marine supply that you can by the nylon at a good price.
If you know where the sailboat dock is at the Galveston Yacht Basin you can buy rope at the shrimp boat supply. The sailboat dock is across the channel from the drystack, fuel dock, yacht service. Really good prices.
fishgetter, I sent you a PM. I have one bought around ten years ago as a spare, never taken out of the package. Professionally made with 15ft of galvanized chain. I believe it was 300ft, 9/16". Need to get rid of it; no longer have the boat.
The ABSOLUTE most inexpensive place I have ever bought anchor rope is at MARINE INDUSTRIAL SUPPLY, (formally the shrimp boat store) in Freeport Tx. They sell it by the pound. The Gores have been in business since before I was born and Im 52