Although it is possible to find white leather sectional sleeper sofas online for less than $3000, be prepared for a piece of furniture with a cheap frame, a cheap sleeper mechanism & mattress and a “bonded” leather.
Hopefully you know enough to stay away from bonded or bicast leathers.)
Unless you are exceptionally lucky (and knowledgeable) you will probably be getting a construction that is the equivalent of a $399 – $799 imported sofa with an expected lifespan of 3 years or less.
Sectional sleepers are considerably more expensive than sofas because they are bigger and because the sleeper mechanisms add substantial additional cost.
Paying a few hundred dollars for furniture that will need to be replaced within a few years is an acceptable trade off for many people.
Spending $3000 for furniture that will need to be replaced within a few years should make you pause and think about what you are doing.
While it is possible to find a mid-quality “leather” sectional within your price range (possibly even with a cheap but genuine leather,) your sleeper requirement drastically narrows your choices.