There's not really a sweet spot for price ... it depends on the bicycle.
In other words, if I want a bicycle that meets certain criteria, that's what I'll get.
Could be an attractive $50 tip shop bicycle ... or a $5000 tandem.
Rowan and I have, I think, 21 bicycles ... if I'm not mistaken. Several are in pieces (frames over here, parts over there) so it's kind of hard to count exactly.
And I have realised just recently that we haven't purchased a pair of new bicycles in a few years. Hmmmm .... might have to fix that problem soon.