Rental space may be too expensive. Rent space from a church. I have been the rabbi of several congregations that rented Religious School space from churches, and one that rented space to a church. It works and is usually the most economical option. In general church education rooms are unused on weekday afternoons, most weekday evenings and on Saturday mornings.
Many churches are happy to rent space at minimal cost.
Some negotiation needs to take place about the issues of Christian symbolism, Jewish art left in classrooms, etc. These issues are solvable. There are other benefits. Such a Jewish presence in a church emphasizes the interfaith nature of our society and reminds Christians of their Jewish roots. Of course, your congregation has to be able to accept this course.