Crispus was the son of Constantine I(The Great), or also known as Saint Constantine. Historians place his death by execution in 326 AD, and estimate his date of birth to be around 295-305 AD.
During the time of Constantine The Great and his sons, roughly around 300-330 AD, bronze coins were originally coated with a very thin wash of silver. This results in the appearance of a silver looking coin, such as in the photo above. Full preservation of this fragile silver layer would have such a coin
command higher values then typical coins from this period of time.
Inscriptions for such a coin are DNFLIVLCRISPVSNOBCAES on the portrait side of the coin, and PROVIDENTIAE CAESS on the reverse. The head on one side of the coin is that of Crispus, and the Roman god Jupiter appears on the reverse.
With Ancient coins, their values are harder to assess due to the unknown number of coins minted, their varying appearances, preservation state, and desirability, but approximate values for the common types run like this:
worn: $10 US dollars approximate catalog value
average circulated: $25
well preserved: $150
It is reasonably rare to find a well preserved Roman coin due to their age and natural wear, such an item could certainly command higher prices then usually estimated due the its rarity in terms of condition. It should also be noted that there are multiple types of these coins, with variations such as the inscriptions, design, or mint mark, each with differing values.
The free to use online resource site Wildwinds provides a reasonably detailed list of the coins of Crispus and many other Roman rulers.