Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.

select title, price, case 
    when pub_id in (
        select pub_id
        from publishers
        where state = 'ca') then price * 1.1
    when title_id in (
        select title_id
        from titleauthor
        group by title_id
        having count(au_id) > 1) then price * 1.05
    when title_id in (
        select title, sum(qty*price) NewPrice
        from titles t
        inner join sales s on t.title_id = s.title_id
        group by title
        having sum(qty*price) > 500) then Price * 1.02                  
    else price * 1.01
    end NewPrice
from titles