400 to 600 dollars depending on condition and where you live.
Don't know the value, however based on proofhouse.com ,it was made in 1973.
On the butt
I found a Colt diamondback with that serial number made in 1971.
1969 value guesstimate around $450
You will need to call Colt to find out.
what is the manufacturing date fo a colt diamondback serial number O72239
Diamondback serial # D69679. was mfg'd in 1975. made about 1976
Made in 1973.
It is found under the breach below the barrel
Need the model number(Model 10,15,40,66,etc.) or, a complete description(barrel length,how many cartridges does it hold,markings on barrel)
100-1000 USD
100-1000 depending on the specifics