Jules,
It is cheaper - depending on where you go. There is a thread on IVF tx in Russia - which costs about £800. By and large, people tend to go abroad for donor eggs - because there simply is not the availability in the UK - however much you can afford.
If you can get IVF tx for 1,800 and the drugs are only an extra £500, then that is a bargain, and if you are happy with this clinic you don't need to go anywhere.
The clinic in London I wanted to go to charged between five and six thousand pounds, and they told me to allow an extra fifteen hundred for meds! So you can see why, even allowing for travel costs, treatment abroad is cheaper.
As Indiana mentioned, other countries also have a higher success rate with IVF too. There was a recent Parliamentary report - another thread on this board somewhere - that said exactly that.
Good luck
Joy