JSFiddle - React, Tailwind, and code Playground

HTML

<div data-bind="with: selectedPrice">
    <p data-bind="text: NetPrice"></p>
</div>
<select data-bind="options: priceList, optionsText: 'NetPrice', value: selectedPrice"></select>

JavaScript

function vm() {
    var self = this;

    self.priceList = ko.observableArray([{
            Id: 1,
            NetPrice: 123,
            IsDefault: false
        }, {
            Id: 2,
            NetPrice: 123.99,
            IsDefault: true
        }, {
            Id: 3,
            NetPrice: 199.99,
            IsDefault: false
        }]);
    
    self.defaultPrice = ko.computed(function(){
        ko.utils.arrayForEach(self.priceList, function (price) {
            if (price.IsDefault) {
                return price;
            }
        });
    });
    self.selectedPrice = ko.observable(self.defaultPrice());
};

ko.applyBindings(new vm());