Stairs...risers imparticular

Are the risers in good shape and sturdy? If so, then all you need to do is replace the treads and paint.

Are these interior or exterior? If you replace entirely, it requires pulling a permit. Do you know how to do that?

Paint is the cheapest, fastest, most impactful idea. To emphasize the stairs, paint the steps one color and the risers a washable white. Paint the bannister in the same contrasting colors, with the rails matching the risers. The second is a runner from top to bottom. Buy two or three inexpensive runners and glue them end to end. Glue or tack them tightly on the steps and on the risers. The third is to use synthetic floor tiles and glue or screw them to the risers. Spanish and French style tiles are popular now. And a fourth option is to hang bright, attractive pictures on the wall going up the stairs. Hang the most striking at your eye level from the bottom, say at 5’6” from the floor, probably about 7 steps up. Any glancing at the staircase will focus on that picture first. This could be the cheapest option if you already have several pictures or posters. Best wishes, and please post your progress on Hometalk.com! 😇

I painted mine. Brown.

You could use Wallpaper and Varnish the Risers - Tiles or Tile Stickers - Vinyl Laminate flooring - Or a combination.............

I bet they gave you permission to re-do the stairs. I hope the owners are paying for the job they should have done themselves. Looks like a tripping hazard.