Custom-made dust covers for stationary power tools don't come cheap. Machine covers need to resist water, provide a little scratch resistance, and be durable enough to survive being taken on and off every few days. Their design needs to be simple, but fit the machine well. The fabric shouldn't tear easily, but does not need to be bullet proof. I did a little looking and found a few alternatives that might save you a buck or two if you chose to make your own machine dust covers.
A.) Off-the-Shelf Options
There are numerous tarp and cover companies that will sell you nicely sewn covers in a wide variety of standard sizes - lots of materials and options to choose from. Expect to pay $100 and up for each cover. These companies make covers for BBQ grills, A/C units, automobiles, generators, riding mowers, snowblowers, fish smokers, and RVs.
grainger.com --> "machine dust covers"
creativecoversinc.com -> "equipment covers"
woodcraft.com or amazon.com --> "HTC machine covers"
B.) Repurposing Options
The dust cover industry is not all that innovative (shocking!), but check out what GenTent Safety Canopies is doing. While you're at it, check the other sites listed below for ideas about re-purposing pre-made covers.
gentent.com --> "stormbracer"
wayfair.com --> "generator covers"
homedepot.com --> "extra large waterproof generator cover"
amazon.com --> "patio table cover"
C.) DIY Alternatives
This soft, fabric-like version species of Tyvek feels nothing like house wrap; its "soft structure Tyvek" without any logos. I found a 4-ft x 150-ft roll for $160.00 online. Check specialty kite supply shops, backpacking discussion forums, etsy, and ebay. Many people are making lightweight, water resistant bags and covers from Tyvek 1443r. Sewing it might be a little tricky, but people do it. Tyvek-specific seam tape is available (seam backer material?).
Tyvek Cargo Covers by MaterialConcepts.com
These reusable cargo covers are sized to slip over a standard-sized stack of stuff shipped on a standard-sized pallet. Several sizes available and reasonably priced (especially if you really like the Tyvek logo).
Fold-Your-Own Poly Tarps
Think origami. Two websites, foldifyapp.com and templatemaker.nl, provide you the tools to create your own templates. You simply plug in the dimensions for the open-top "boxes" that will become your machine covers. Use the dimensions on the resulting print out to fold a blue polyethylene tarp into a cover. Best to go with tarps in brown, green, or silver if you have a wife and/or want to remain on speaking terms with the neighbors. Try using pound-through grommets and thick waxed thread sold at marine hardware stores and sailing gear shops.
Hire a Local Seamstress
Check Craigslist for people advertising custom sewing services. If you provide the dimensions (maybe a PDF template) and the fabric, you will probably save yourself a bundle.
String-reinforced Poly Sheeting
This stuff is tough, reasonably unobtrusive looking, and fairly affordable. If you're into sewing your own durable dust covers, give this stuff a look.
These mesh tarps/blankets are commonly made of knitted HDPE polyethylene fabric and have finished edges and grommets. I have seen a 16-ft x 20-ft option for $50.00 on Amazon - affordable enough to cut it down as you would fabric by the yard.