The best price I found a couple of years ago was for Agribon brand, that Johnny's sells. I did a search with Google for "agribon row cover" and as I recall one source was much cheaper than all the others, so I bought a roll, but I don't recall the details--I just looked at the box and the remaining part of the roll but I didn't save any labels. I THINK that I got a 250 foot long by 83 inch wide roll of a medium weight stuff. We use it some years on strawberries for frost protection, and it has lasted a few years so far, with taking it off when it isn't needed any more. Tulle won't provide any frost protection.
A local hardware store here carries small pieces, 8'x10' of AG19.
I use both weights, one for frost protection (AG30 ~1oz) spring and fall and then a lightweight one (AG19, ~.5oz) for insect and bird control. I may switch and use AG50 for frost protection.
One of the local nurseries uses the heavier weight AG30 as tree wrap during transport of larger trees. They will sell cut lengths by the ft2. So you might check with larger nurseries...
Our Denver greenhouse and agricultural supply companies sell Agribond in long rolls. It was about 5x more than I needed (7'x250' roll). I may go ahead and get a roll of each since that is still cheaper than buying the smaller pieces and I need to replace some of the damaged cover I had been using.
Johnny's is a good source though after shipping kinda pricey for me. There are others such as Vesey's, Drip Works, Agricultural Solutions, Greenhouse Supply, etc. There might be some one close to you.
Google is your friend...