Debby... Hi.. and welcome.
Your best bet is to keep your eyes open and make sure to follow the deals and freebees thread. There are alot of books given away or very cheap ($1) if you keep an eye out. Granted you would have to read what is available, but alot of the books are very good.
Take a look in our Wiki for places to get content
https://wiki.mobileread.com/wiki/E-book_stores
And also for places with free books
https://wiki.mobileread.com/wiki/Free_eBooks
In addition there are several thousands of books in our d/l section. Click on the "E-Books" like in the blue menu bar at the top of every page here. If you like mysteries, have you read all the Sherlock Holmes books?
Finally you are able to borrow books from the Library with your Sony. Not everyone has a local library that has alot of ebooks. But, for $100 a year you can get a non-resident NY library card. They have ALOT of ebooks... this would be a way to get the more contemporary books for free (almost.) Once again, check our Wiki at
https://wiki.mobileread.com/wiki/EBook_Lending_Libraries
Hth,
BOb