Want to install a single (or maybe two) not too large or fancy small
whip-type "all-band" antennas on the eaves of a residence and run cables
to BNC jacks inside, for scanner listening in the 25-50 MHz, 100-160
MHz, and 450-490 MHz bands, and am trying to decide between a less
desirable antenna and scanner location but with only about 3 to 4 meters
of cable run, or a more desirable location for antenna and scanner but
with maybe 7 to 10 meters (25 to 30 feet) of cable run.

Question is, if I use good 50 ohm coax how serious would the cable
losses be for 20 to 30 feet of cable in the above bands (with the
100-160 MHz band probably the one of most interest)?

Use any cable 1/4 inch or more in diameter , YOu will not notice it up to
500 mhz for only 30 extra feet. Best bet is some rg-6 cable if you can find
some that has a copper shield or if you have a good way to make a connection
to the shield as some is aluminum. RG-8x is good for a short run. Don't
worry about the impedance of 50 vers 70 ohm cable. It will not effect your
receiver coverage.