I'm a later-40-something non-running-ish triathlete with a problematic achilles so I am presently limiting my running miles to perhaps one day get over my achilles problem.
That being said: yay bikes
current stable: [from fave to least fave]
Domane [endurance aka relaxed geo road bike]
Diverge [adventure/gravel-ish]
Bullit [old school full squish mtb, w/180mm downhill oriented fork]
cervelo P2C old school TT bike [in the before times, was my race day tri bike]
all of these are 1k or less on craigslist
I do around ~100 mpw just to stay in shape and have fun. My running is very limited now but I do get out every week if the injury permits it.
The reader will note there is not a pure roadbike in my stable. Thats for a reason. I'm old and inflexible and endurance drop bar roadbikes offer everything you might want [speed, comfort] in a road bike and they are especially useful for longer rides [50+ miles] and not being beat up like aero position would on a roadbike or TT bike
my budget for all these bikes is like 4k, I do enjoy the diverge a bit as in my area I can do a mix of road, and fire trail on the same bike and not beat the f*ck out of my domane , lots of loops near me permit the off-road meandering loops yours probably do too