Most of us here quilt on domestic machines, meaning the typical machine for home use. You don't have to purchase a longarm in order to machine quilt even very large quilts.
The biggest limitation on using a home machine is the harp size. This is the area between the needle and the right hand side of the machine that limits how much quilt sandwich you can stuff in there. Most machines can handle a twin-size bed quilt if the batting is not too thick; I loosely accordion-pleat the quilt in there.
For very large quilts, it can be a good idea to split up the batting to cut down on bulk under the machine's arm. Marti Michel has a book out on how to do this, although I first saw the method described in detail in one of Debra Wagner's books. Basically you layer the quilt as usual, fold back top and backing out of the way, and "S"-cut the batting into thirds. You baste and quilt the middle third of the quilt first. Without the batting under the machine arm, it is easier to do this. Once the middle is quilted, you re-attach one side of the batting, baste that side together, and quilt that side. Do the same on the other. The result is a large quilt that has been completely machine-quilted on a domestic machine, with no clues that it was done in sections.