Whitening doesn't have to be very expensive to get a decent result. It depends how sensitive your teeth are. If they are very sensitive, then you'd be better getting a whitening product from your dentist, they'll have access to a greater range and there are now some formulations that are pain-free even for people (like me) with very sensitive teeth. However, this will be more expensive than a product you can just buy in any shop. If you don't have any problems with sensitivity then you could try something like Crest whitening strips, they're the most impressive results without professional treatment, I'd say. Get the ones from the USA, you can buy them on Ebay.
For your tooth straightening, you'd be looking at something like Invisalign, which runs about £1500 per upper/lower arch. So for just the bottom teeth, maybe around a grand and a half. Not cheap, but that's the going rate. You will have to wear a retainer to bed to maintain results even after treatment ends.
The bridge replacement is completely variable, I don't know how many teeth it's replacing etc so you'd need to see a dentist for an exact quote on that. Be sure to do these things, like bridge or composite, AFTER your whitening, so they match to your 'best' and current tooth shade, would be silly to do it after.
Composite bonding can be great, I've had it done but I worked for a dentist at the time, so got it at a very reduced rate. I think he ordinarily charged £500 per tooth. Look in the mirror and smile, count how many teeth are visible when you smile naturally - it's only really those you'd need the bonding on so you can work out a ballpark cost from there.
I know a lot of people travelling abroad for dental work these days as it's more affordable, but that would be your call to make and I'm not necessarily advising that, just something to look into perhaps but be aware of the risks.