Try some of the 'discount' airlines such as EasyJet (based out of Luton - no frills but clean and cheap); GO (based out of Stanstead - owned by BA) or RyanAir.
I just had a look through their web-sites and managed to get London-Amsterdam for £56 ($90)return. London-Dublin £49 ($80) return.
From the charters (Britannia; Air2000 etc) UK-Spain £79 return ($125) etc.
My price-per-mile comparison was based on the imformation published in Business Travel World, which compares information provided by IATA/CAA/EC. And consistently shows that there is virtually no difference between US Domestic and inter-european fares.
The current trend is that inter-european fully-flex fares have increased by 15% over the last 12 months (ie. the airlines are hitting the business traveller) but price-per-mile has come down by 7% (mainly due to the increase in discount airlines).
There are bargains out there to be had. You need to know where to look - many of the discount airlines keep their prices down by NOT dealing with travel agents, so your travel agent (or web agent) will not be able to find the fares for you, you have to look at the propriatory web sites.
I think that there is a concensus that the Europeans expect better service than the American's. The US carriers certainly readily accept this - as many of the posts on this site testify. That is why Rudi and I get comp lounge access (ie. Free Red Carpet Club), because the US airlines understand that we would not expect to pay for that.
I'm hoping for some feed-back on this, but my experience is also that if you fly into the US from Europe and transfer to an onward US domestic flight, you are also likely to get upgraded. The US carriers will also give Europeans lounge access and beverage 'tokens' for their lounges which a US flyer would not get.
MF