I like all the 70's Realistic receivers, and nearly all can be be characterized as low/mid-level.
I have a Sansui 771 that qualifies as well.
I also have an Onkyo TX-3000, which is really terrific. However, the Onkyos of this era are not terribly common.
I really like my little Sherwood S7100-A, but that is at the low end of the power scale.
Pretty much any good-quality 70/early 80's-era receiver in refurbished state of repair will sound great.
I have several midrange receivers from the 70's, all of which I recapped.
With a few tweaks of the tone controls, in AB comparisons, I can make them all sound identical.
I would look for something in excellent cosmetic condition, and not worry much about brand name.
Condition is key.