UX Audit for new charity website

We need a UX audit carried out for a new UK charity's website (recently gone live). We built the site but want an objective audit by someone other than our own team. Whilst there are plenty of agencies available, the majority seem to charge the earth for what strongly appears to be automated content. Thus, we're really looking for someone who can understand the charity's purpose and conduct an audit of its site with this sympathetic, objective view in mind.