Plain fabric or vinyl with no nap will be the least, a plaid, stripe or print with a repeat can take quite a bit more.
Having really good upholstery professionally done can be expensive (taste throw up in the back of your throat expensive!)... but "do it yourself" is for a pretty experienced seamstress/tailor.
Sail Rite sells heavy duty machines, fabric AND has excellent how to videos that would show you how to measure for fabric, how to make piping, and how to make patterns for the cushions, etc.
if memory serves.