Well, we took your advice and did this on the PHP side, except not with Extra Fields.
We custom added a new data field "dealer_cost" to the xcart_products array using phpMyAdmin, then went into include/product_modify.php and added
Code:
'dealer_cost' => $dealer_cost,
after
Code:
'title_tag' => $title_tag,
around line 900
and added to main/product_details.tpl after List Price
Code:
<tr>
{if $geid ne ''}<td width="15" class="TableSubHead"><input type="checkbox" value="Y" name="fields[list_price]" /></td>{/if}
<td class="FormButton" nowrap="nowrap">{$lng.lbl_dealer_cost} <span class="Text">({$config.General.currency_symbol}):</span></td>
<td class="ProductDetails"><input type="text" name="dealer_cost" size="18" value="{$product.dealer_cost|formatprice|default:$zero}" /></td>
</tr>