Would you please offer some information about having one's quilt quilted by someone else? Is there a ballpark figure, estimate or some kind of cost range? Thank you in advance for your answers.

In my neck of the woods it is .015 to .02 per sqaure inch for basic quilting , Custom is a whole different subject can go as high as .10 per square inch.
It depends on if you are supplying the batting , backing , thread and if you want them to do the binding. In my area these are all above the basic costs.
There are plenty of longarm pros on this board who would be happy to provide a quote. Special section in the classified just for such services.

A lot depends on your area and the type of quilting you want on the quilt.

It realy has to do with the type of quilting and what the going rate is in your neck of the woods.. I start my prices at .015 for longarming and offer dicsounts for various things and times of the year.