I have the Tin Lizzie 18, the older model. There are others on this forum who have the Tin Lizzie 18 LS, the newer machine. They are good basic machines with enough throat space and side to side frame space to quilt large quilts. They come with most of the bells and whistles at a much lower price than the high end machines. I am very satisfied with mine.
That said you should try one and other brands as well before buying. Check-out the Tin Lizzie forum on Yahoo. Check-out the Home Quilting Systems forum and forums for any other brands you are interested in. Investigate the possibility of a used machine with warrenty from a manufacturer.
Quilting for others is a nice goal but it will take you quite a while to get good enough to charge for your work. It isn't as easy as it looks to keep your customers happy. There are also forums for professional quilters. Be informed before you make this big purchase.