Some suggestions:

Buy a half gallon Hudson sprayer and mix only what you need. It's never a good idea to store excess spray mix, most fungicides are unstable when diluted with water and will lose at least some efficiency over a week's storage, and storing fungicides in anything except the container they came in is against federal law.

The three cheapest fungicides that are worth anything at all for blackspot are probably horticultural oil (Sunspray), plain old canola cooking oil, and wettable sulfur. Typical results when these are sprayed weekly would be something like 5-10% leaves with blackspot compared to 30 to 40% for the unsprayed control. These are results for controlled, university-run tests, in Oregon and Delaware. If blackspot is a serious problem in your part of Florida, you might get much poorer results.

For only 6 roses, get a can of Rose and Floral spray. It has insecticide and a fungicide and spray your roses once a week using that. Make sure to spray the undersides of the leaves well. Or get so of the Bayer All in one product and use that. If you already have blackspot you will need the dithane to clean it up. Use it every three days for three weeks. That should kill the spores.

Thank You Mike and Dan, got a lot more information that I was unaware of, Thanks for You time Fellas, Very Much Appreciated.
Fred