I too recently acquired a pair of Heresy 1's and am currently driving them with a modified Dyna Stereo 70 - (theoretically 35 watts per channel).
In my room which is 19.5 x 14.0 ft. and being seated 11 ft. from them, I find it provides a wonderful match. In my opinion, any decently designed tube amp having 15 or more watts per channel, (maybe less, since the Heresy's are fairly efficient), would be fine and may be "findable" within your budget; so good luck.