Button available when filling fields

First you put the "disabled" attribute to disable the button. Then you verify with javascript if all fields have been filled, if so, you enable. With a single field, it would basically be like this:

$("input[type=text]").on('change', function() {   
  if($(".nome").val()) {
    $(".send-quote").prop("disabled", false);
  }
});

Already with all your fields, I set up there in your jsFiddle

html

<h2>Quero um <span>Automóvel</span></h2>
                        <div class="form">

                            <h4>Valor do consórcio: <span class="slider-value quote-form-element" data-name="Valor | Automóvel"
                                    data-slider-id="consorcio-auto">R$ <span></span></span>
                            </h4>
                            <div class="slider" data-slider-min="20000" data-slider-max="100000" data-slider-start="23192" data-slider-step="1000" data-slider-id="consorcio-auto"></div>

                            <h4>Seus dados:</h4>



                            <form name="cadastrar">
                            <input type="text" id="idNome" onchange="validarCadastrar()" name="Nome" placeholder="Nome..." class="quote-form-element" />
                            <input type="text" id="idCidade" onchange="validarCadastrar()" name="Cidade" placeholder="Cidade/UF..." class="quote-form-element quote-form-client-email last" />
                            <input type="text" id="idTelefone" onchange="validarCadastrar()" name="Número de Telefone" placeholder="Telefone..." class="quote-form-element telefone" data-mask="(00) 0000-0000"
                            />
                            <input type="text" id="idEmail" onchange="validarCadastrar()" name="Endereço de Email" placeholder="E-mail..." class="quote-form-element quote-form-client-email last contact_email"
                            />



                            <h4>Política de Privacidade</h4>
                            <div class="checkbox quote-form-element" data-checked="yes" data-name="Política de Privacidade">

                                <span class="checkbox-status"><i class="fa fa-check"></i></span>
                                <span class="checkbox-values">


                            <button id="idButton"  class="button button-navy-blue send-quote" type="submit" disabled>Simular meu consórcio <i class="fa fa-paper-plane-o"></i></button>
</form>

js

function validarCadastrar(){
var nomeVazio = idNome.value;
var cidadeVazio = idCidade.value; 
var telefoneVazio = idTelefone.value;
var emailVazio = idEmail.value;

if( !(nomeVazio == "") && !(cidadeVazio == "") && !(telefoneVazio == "") &&     !(emailVazio == "") ){
document.cadastrar.idButton.disabled=false;}

else{
    document.cadastrar.idButton.disabled=true;
}

}