When you say you spray basted, do you mean that you actually sandwiched the back, batting, and top? And when you say you want to send it out to be quilted, do you mean to a longarmer? There are some people who quilt for others using their domestic machines (the owner of my LQS was one of them until she recently got a longarm) and they might be willing to take the quilt already sandwiched. A longarmer will want 3 separate pieces - back, batting, and top - because of the way the quilt must be loaded onto the longarm, and will probably not take them if they are sticky from the basting spray. But washing a top implies also having to dry and press it. The drying can be done by laying the top flat on towels or blankets to dry, but pressing could be an arduous task, depending on the complexity of the piecing.
I have never used basting spray, so I don't know how it feels. Is it possible to take the 3 layers apart without damaging them? If you do, is the fabric sticky?
Is it possible that you could find someone with a sit-down longarm who could finish the quilt for you? Or perhaps someone with more experience could quilt it on her DSM, or show you how to accomplish it? I quilted most of my tops in sections before I got a longarm, but I did quilt one large quilt (not in sections) on my DSM, so I know it can be done, and I would try that again before I would wash an unquilted top.