As stated, "how longs a piece of string". Important thing to remember is most developers are pretty bad and if you're paying some kid £500 quid for it, you might never get anything, so lets pretend you're dealing with market rates.
Single band contractor £250-350 a day. Then it's about how long you're giving them, again this can be highly variable depending on what you actually need done, but generally they'll quote 6-8 weeks or 3 months depending on how complex and how much of a pain you are to deal with.
So basically between £7500 - £16250 on the lower rates, which is alright if you're outside of London. A freelancer should be about the same, an agency will try and double those quotes, while people who are desperate will be willing to charge less.
Most folks opt to desperate in the first instance as they don't consider their developers gotta eat, but rest assured, theres enough businesses paying market rate for everyone who's good to earn decent money.
Obviously it depends on the specifics, but you asked to pull numbers outta our **** so I did.
What an odd site ... Drupal CMS with responsive front-end points at someone who knows what they are doing.
Badly configured DNS records and no page title begs to differ.
Guy that made site is probably not the guy who hosts site.