Most basements have a cement or concrete floor. If it’s level, the cheapest solution is to just use that as your floor, maybe covering it with rugs or a roll of vinyl flooring. If the concrete is not level or smooth enough you can add a thin layer of new concrete on top of it and smooth it with a trowel as you apply it. You can also add pigments to concrete to color it if you want a shade other than basic gray – such as terracotta, beige, or charcoal. Another option is to buy paint made for porches and patios and apply it over a primed water-sealing undercoat. You can find that kind of paint at a home improvement store, starting around $35 a gallon.
The basement depicted here had unused space underneath the stairs. Why not transform this area into a storage or display area instead? These homeowners found some usable square footage in their home by remodeling their basement into a space-conscious hangout, an inventive and creative strategy that shows you don’t have to substitute style for function. 
Estimate the overall cost to install drywall in the basement at approximately $1.50 per square foot. The basic drywall panel measures 8-feet tall and 4-feet wide and is available in thicknesses that range from 1/4" to 5/8". This standard panel usually costs between $10 and $20. Price will vary depending on the brand, panel's thickness, and if it has any special features like mold resistance which may be beneficial for a basement space. Other material costs when adding drywall include the hardware to secure it to the framing, joint tape, and drywall mud.