I'm led to believe Van Aaken Developments can turbocharge the new Fiesta 1.4 and 1.6's for around half your budget, although it's not listed on the website. If you want to give them a buzz, you can get their number from
www.vanaaken.com.
Also for tuning and engine swap jobbies,
www.pumaspeed.co.uk or
www.pumabuild.co.uk are both cited as being quite good.
Hopefully someone should be able to give you the excitement you crave at a price that's nice.