Selling house, and want to put in the easiest lowest cost patio in backyard
My recommendation is to not put in the patio.  Your efforts may lower the value to the buyer rather than raising it, especially if what you're planning to put in is the "easiest, lowest cost patio" rather than a landscaping masterpiece.  

Like many kinds of projects, you will almost never get a financial return from the work and investment unless:


you understand the real estate market and know what will add value to your house
do those very targeted projects
have professional-level skills  


Even worse, the buyer may have other ideas about what would be ideal for them.  You could end up saddling them with something that isn't what they want and doesn't meet their needs, or even something they then need to spend money and time on ripping out.  

Even if you do the right projects, if you don't have professional-level skills, anything that comes out looking like a "homeowner special" will scare off buyers.  

Putting your house on the market is a lot of work to do it right.  Don't wear yourself out doing projects that don't count.  Bring in a real estate agent or professional house stager to get advice on how to best prepare to showcase the house.  Putting in a patio isn't likely to be on the list.

You could even offer to knock the price down a little to reflect the savings and value of your time to not do a patio, which may be even more attractive to many buyers than your doing the work.