I wouldn't base too much on that poor bounce rate. What you need is to target UK folks who are actively looking for holidays, I'm not sure Stumbleupon is a great way to do this.
Here's my thoughts UI wise
1. You need to learn more about your market, or maybe you already know this but have yet to put it into practice.
Start with one particular user, let's say John. John is an Adwords guy in Google. He is 28 and wants to go on a summer trip with his girlfriend. By an exercise left to the reader John has found your site. John needs to go away in August as that's when downtime is for his team, and he's hoping spend about £400 or thereabouts, though he will pay more for a better place.
Based on John alone, here are a few random thoughts.
1. It's a bit funky to drag end of the slider on top of another just to say "August". Also I think you should consider handling custom date ranges.
2. Sliders aren't a great mechanism in my opinion, as they don't tell you what you're missing out on. Possibly a histogram behind them would help. (See Year or Price on this page http://www.carzone.ie/ to see what I mean)
3. People don't book package holidays in isolation. John should be able to input "10th of August for 7 nights, less than £600" and then send this to his girlfriend, or post it to Facebook, or do whatever so that John and his group can make a decision. (This is especially true for package holidays)
4. Ditch the sliders (hey I said these thoughts were random). You must realise your slider for selecting stars was a bad idea when you were coding it.
5. Spent more time on designing your search results page. Basically when someone clicks the little bubble and gets a list of 5 packages, they inevitably have to bounce into and out of each of them to assess them. This isn't a great experience. The more info you can offer up front the better.
Overall great job, I think you've done some good work, and the stuff I've wrote about is relatively minor in comparison to the significant challenge of getting the traffic you need.
Best of luck, Des