That should do it. Trimmed down a mod of mine to do it.
2 plugins, 1 template. Template's cached. Only shows the link if the ID exists. All you have to do is to edit the template (Link In Postbit), change the field IDs to the correct ones, and that's it.
I made it a product and here's a link to it:
https://vborg.vbsupport.ru/showthread.php?t=218293
Change the template to below for what you need (specifically a known URL + a profile field).
Code:
<if condition="$post['field1']">
<a href="http://www.battrick.org/nl/office.asp?userID=$post[field1]">$post[field2]</a>
</if>