I would like to make Bordeaux mixture for use as general purpose fungicide. I would be preparing stock solutions of copper sulfate and hydrated lime. I was able to find hydrated lime from specialty nursery but I couldn't find copper sulfate anywhere. They are available from eBay, mostly in reagent grade quality and are therefore as expensive as gold. I don't want really pure copper sulfate, perhaps an 80 to 90% purity is good enough for use as fungicide, provided the impurities are harmless or inert.

Any leads on where to buy low purity very cheap copper sulfate powder?

Here's a fantastic recipe for making the Bordeaux mixture using the stock solution approach. Major advantage is that the stock solutions can be stored indefinitely and the Bordeaux mixture can be quickly assembled:

The old-fashioned way of making a Bordeaux mixture is to prepare "stock" solutions of lime and of copper sulfate that are later mixed by pouring them into water in the sprayer. This method also works best for making small quantities of Bordeaux. Using a plastic bucket, dissolve 1 pound of copper sulfate in 1 gallon of water. This solution can be stored indefinitely in a stoppered glass container.

Then mix 1 pound of fresh hydrated lime in 1 gallon of water. This mixture needs to stand for about 2 hours before use. This mixture may also be stored indefinitely in a stoppered container. Preparing a stock mixture of lime eliminates the need to obtain fresh hydrated lime each time Bordeaux mixture is prepared.

Be sure to clearly label both stock solutions and store them where children cannot get into them; these materials, especially the copper sulfate, are very toxic and corrosive.

To make 2-1/2 gallons of a 10-10-100 Bordeaux mixture, measure 2 gallons of water into a plastic bucket. Because the materials are already in solution or suspension, the order in which they are added to the water does not matter. Shake the stock lime mixture and add 1 quart to the 2 gallons of water. While stirring with a wooden paddle, add 1 quart of the stock copper sulfate solution. Continue stirring for several minutes before pouring into the sprayer. The mixture is now ready to use. Be sure to constantly shake the sprayer while using it to avoid clogging. Read the label directions carefully on the copper sulfate regarding the proper protective equipment to wear when preparing the stock solutions as well as when spraying.

This formulation of Bordeaux mixture will be adequate for practically all home garden needs. If you wish to maintain Bordeaux mixture on a tree throughout the entire winter rainy period, a slightly stronger mixture (1-1/2 quarts of each stock solution to 2 gallons of water) may be used. In spring when the buds are breaking or on sensitive plants, use a slightly weaker mixture (1 pint of each solution to 2 gallons of water) of Bordeaux, or use a fixed copper spray.

But then the cost of copper sulfate powder is beyond the moon... I know these can be cheaply obtained but where oh where on earth?

Now that I was pressed for time to spray around the Super Bowl event, so I bit the bullet and bought from eBay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=270208076126&ssPageName=STRK:MEWA:IT&ih=017

It would still come out cheaper than having to buy the pre-mixed non-organic fungicides.

Agway used to carry it. Don't know if they still do, but worth a try.

You can buy Copper Sulfate technical grade at Univar Corporation in South San Francisco, California. Univar used to be called Van Waters and Rogers. - Millet