I think “less” must refer to cost only, in this case. When comparing costs, one is “less” or “more” than the other; when comparing tech levels, one is “higher” or “lower” than the other. For example, Circle of Life allows you to replace a card with one that’s “one tech higher”, not “one tech more”. If the second interpretation was intended, it would be “a unit of the same tech level or lower and the same cost or less”.