In this video I compare a brand new set of double bass strings with an identical brand that have been on my bass for a year and a half. I discus the topic and share some examples of pizzicato and arco playing.
The strings I use in the video are Evah Pirazzi Weich by Pirastro. I'm a big fan and recommend them if you are looking for a hybrid string. I usually change them about once a year, but please bear in mind that some brands can last much longer, especially steel strings like Thomastik Spirocore.
It really comes down to personal taste, so you may not need to shell out for a fresh set as often as you think.