Variant Prices are loaded through JavaScript using the "product_price" id. Try the code as it is below. I did not test this, and it may cause a Javascript error, in which case I believe you will need to edit the skin1/modules/Product_Options/func.js file.
Code:
<tr><td class="ProductPriceConverting" valign="top">{$lng.lbl_price}:</td>
<td valign="top">
{if $product.taxed_price ne 0 || $variant_price_no_empty}
{* THIS IS THE LOGIN REQUIREMENT *}
{if $login eq "" or $user_membership ne "Wholesale" }You must be logged in as a wholesale buyer to view prices.
{else}
<font class="ProductDetailsTitle"><span id="product_price" style="white-space: nowrap;">{include file="currency.tpl" value=$product.taxed_price plain_text_message=true}</span></font><font class="MarketPrice"> <span id="product_alt_price" style="white-space: nowrap;">{include file="customer/main/alter_currency_value.tpl" alter_currency_value=$product.taxed_price plain_text_message=true}
{/if}
</span></font>