JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://code.angularjs.org/angular-1.0.0rc4.min.js"></script>
  <div ng-app="myModule">
    <div ng-controller="DefaultCtrl">
        <form name="myForm"> 
            <input name="salesPrice" type="text" ng-model="salesPrice" base-price-validator="">
            <span ng-show="myForm.salesPrice.$error.basePriceValidator">This is not valid base price!</span>
        </form>
    </div>
</div>

JavaScript

var myModule = angular.module('myModule', []);
myModule.directive('basePriceValidator', function() {
    return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
            ctrl.$parsers.unshift(function(viewValue) {
                if (viewValue == '2,10') {
                    // it is valid                    
                    ctrl.$setValidity('basePriceValidator', true);
                    return viewValue;
                } else {
                    // it is invalid, return undefined(no model update) 
                    ctrl.$setValidity('basePriceValidator', false);
                    return undefined;
                }
            });
        }
    };
});

function DefaultCtrl($scope) {}