Hi,
The prices fields accept only decimal values.
This need to be done on a template basis.
If you're using the "default" template, in "includes/single-product.html" you'll need to update your file as follow : remove or comment this part
<div class="price-container row" itemprop="offers" itemscope itemtype="http://schema.org/Offer">
<meta itemprop="category" content="{category attr="title"}">
{* Issue #2525 Remove itemCondition need improvement (not used like this) *}
{* List of condition : NewCondition, DamagedCondition, UsedCondition, RefurbishedCondition *}
{*<meta itemprop="itemCondition" itemscope itemtype="http://schema.org/NewCondition">*}
{* List of currency : The currency used to describe the product price, in three-letter ISO format. *}
<meta itemprop="priceCurrency" content="{currency attr="symbol"}">
<link itemprop="availability" href="{$current_stock_href}" content="{$current_stock_content}" />
{if $IS_PROMO }
{assign var="combination_count" value={count type="product_sale_elements" promo="1" product=$ID}}
<span class="special-price col-xs-6"><span itemprop="price" class="price-label" content="{$BEST_TAXED_PRICE}">{intl l="Special Price:"} </span><span class="price">
{if $combination_count > 1}
{intl l="From %price" price={format_money number=$BEST_TAXED_PRICE}}
{else}
{format_money number=$BEST_TAXED_PRICE}
{/if}
</span></span>
{if $SHOW_ORIGINAL_PRICE}
<span class="old-price col-xs-6"><span class="price-label">{intl l="Regular Price:"} </span><span class="price">{format_money number=$TAXED_PRICE}</span></span>
{/if}
{else}
<span class="regular-price col-xs-12"><span itemprop="price" class="price" content="{$BEST_TAXED_PRICE}">{format_money number=$BEST_TAXED_PRICE}</span></span>
{/if}
</div>
and replace it with
<p><a href="/your-target-link">Ask for price</a></p>
for example.
You'll need to change the product.html template file too.
Nicolas