<script src="https://code.jquery.com/jquery-3.6.1.js"></script>
<form id="Form" method="post" action="">
								<div>
										<label for="id1">Поле1</label>
										</div><div>
											<input type="text" name="id1" id="id1">
										</div><div>
									<label for="id2">Поле2</label>
									</div><div>
										<input type="text" name="id2" id="id2">
									</div><div>
									<label for="id3">Поле3</label>
									</div><div>
										<input id="id3" name="id3" type="text" data-rule-required="true" placeholder="100.00" data-marker="3" pattern="[0-9]{4,15}\.[0-9]{2}" />
									</div><div>
  <label for="all">Поле для вывода объединенных данных</label>
  </div><div>
  <input type="text" name="all" id="all" minlength="17" data-rule-required="true" data-msg="Не все данные заполнены верно" required>
  </div><div>
										<button type="submit" name="signup" value="Отправить" id="send">Отправить</button>
                  </div>
	</form>
body {
  text-align: center;
}
const selectors = '#id1,#id2,#id3';
const update = () => $('#all')
  .val(
    selectors.split(',')
      .map(selector => $(selector).val())
      .map(value => {
        if (value.match(/^\s*$/)) return '_';
        if (value.match(/^\d*[\.\,]?\d*$/)) {
          return Number(value.replace(',', '.')).toFixed(2);
        }
        return value;
      })
      .join('-')
  );

$(selectors).on('input', update);

External CSS

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External JavaScript

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