Hi there Fred, thanks for posting a picture (as they say, its worth a thousand words).
The best way to get that dent out, would be to use a round-headed hammer and a dolly - this kit can be purchased for around £20 from Machine Mart (if you wanted to tackle this yourself) - I have one of these kits myself, and can vouch for their suitability for this type of repair.
Essentially, if you were doing this yourself, hold the dolly firmly against the 'outside' of the dent, and gently tap the dent out from the inner edge, using one of the hammers with the rounded head. You need to avoid putting pressure on the cracked paint, as this will just flake off.
I would then clean up and treat the corroded areas with KURUST, leave a bit to dry, and apply some paint to fill in the gaps - I wouldn't spray this - it'll be a nightmare trying to get it to blend.
If you wanted a price from me; I'd charge 1.5 hours @ £40 per hour + £10 call out = £70 (less your discount of 15%) = £59.50.
Call it £55 plus a can of diet coke and a bacon roll!
That includes all my materials (plus you get the remaining paint as a touch-up), you've probably priced that already.
I'm always realistic about the result that will be achieved - I'm not going to say it'll be 'perfect', but it will be as good as possible, and by keeping the repair area as small as possible - it will be far less noticeable.
Have a think about it - if you decide to do it yourself, let me know how you get on, and ask as many questions as you need.