I suspect there are lots of homes with dining chairs like this and I suspect many are in a similar condition...
At my customer's request I used dropcloths for this set of four dining chairs. I bought them at Lowe's and used the 10 oz weight.The entire project took one 9x12 and one 6x9. I pre-washed all in hot water and a hot dryer at the laundromat.
Here's the after:
It's a one million percent improvement with approximately $10 worth of fabric per chair. This is the only chair I have to photograph. The other three remained at home and I made 4 identical slipcovers. Hopefully I'll get a photo of the entire set.
And here's the inspiration photo: