Tallbald,
avoid pressure washing the tires it's very easy to damage one and NEVER
use Armor All on any tire EVER it actually causes them to crack more over
time.
Can't guess the price without knowing the sizes but if it's been kept out of the sun and the cracks appear to be minor I wouldn't be in a hurry to replace them. Actually tubes are more common the larger that tires become and I
wouldn't tube them unless there's some minor problem best determined by
an experienced tire dealer. As suggested windshield fluid or a mixture of
diluted dish soap and water in a spray bottle will show you where the leaks are if they're losing any air. Extremely deep cracks showing cord do need to be replaced as they can be dangerous if they blow out when someone is near, quickly escaping air causes dirt and objects around it to hurl through the air possibly hitting someone maybe losing an eye.
Wear safety glasses and use an air pistol to break loose dirt in places the brush won't reach and it works well around grease zerks too getting the dried grease and gunk off before using the pressure washer it will speed up the job using less water which you don't want to get inside anything. A large flat bladed screwdriver in hand to poke and prod helps too while blowing off the caked on dirt.
Good luck and have fun bringing it back to a shining star.
Al