3rd Party Security Services

I have security concerns with my current hosting of eCommerce sites. The hosts responses to my specific concerns are vague and unsatisfactory. Even when anomalies are pointed out, ( i.e A traffic domain was suddenly pointing to an IP on a server in another country) they return answers like, "Yes, there was a problem, but its all fine now."

I have considered moving to a new host, however, for price reasons, I like my current host.

This has caused me to consider having the security of my server checked and perhaps managed by a third party.

I have no experience with choosing such a service, and research so far has raised more concerns than answers as to how and what may happen by requesting the use of such a service, the reputability of said service providers, and the costs of implementing the recommendations etc.

My main concern is to do with Mysql database manipulation and DNS manipulation within the network. However, a general server vulnerability assessment would be assumed beneficial.