Yes, You an do that. In the exit event of the NumericField you can use the following script.
if (this.rawVale >= 500.00)
app.alert("Please enter a value less than 500.00");
this.rawValue = "";
You can simply restrict the leading and trailing digits by selecting check box and setting desired limit.
Limit Leading Digits>> Max500
Limit Trailing Digits>> Max:2
You can get this option in object pannel> Field of decimal field object in designer.