HTML:
<form>
<fieldset>
<p>
<label for="selectType">Type:</label>
<select id="selectType" name="type">
<option value="Hotel" data-cost="40">Hotel</option>
<option value="Restaurant" data-cost="80">Restaurant</option>
<option value="Casino" data-cost="35">Casino</option>
</select>
</p>
<p>
<label for="selectLevel">Level:</label>
<select id="selectLevel" name="level">
<option value="1" data-cost="0">1</option>
<option value="2" data-cost="15">2</option>
<option value="3" data-cost="30">3</option>
</select>
</p>
<p>
Total Cost: $<span id="cost">0</span>
</p>
<p><input type="submit" value="Go!"></p>
</fieldset>
</form>
jQuery:
$(function() {
$("#selectType, #selectLevel").change(function() {
var type = $("#selectType"),
level = $("#selectLevel"),
cost = $("#cost"),
typeCost = type.find(":selected").data('cost'),
levelCost = level.find(":selected").data('cost'),
total = typeCost + levelCost;
cost.html(total);
}).change(); // invoke the .change() trigger
});
See it in action here
You might want to also set something like "data-multiplier" for the level... whereas level 2 may have a 1.5x multiplier, and level 3 may have a 2x multiplier. You'd have to adjust the jQuery accordingly as well (total = typeCost * levelCostMultiplier, for example).