Hi Alan,
If you're feeling a bit impecunious, a boring head isn't a particularly difficult thing to make. I made mine from two slices of 2" bar on a 3MT blank arbor. Dovetails and a gib strip, a simple arrangement with a 1mm pitch screw to adjust it, and some 3/8" holes for boring bars.
I have seen a further simplification using rectangular slide surfaces.
Perhaps one of the best home-made accessories considering the ratio of effort required to price of a new item.
Neil