Funny enough my European friends use VPNs to shop from USA IP addresses because they think that we always get cheaper prices….

Anyway, An “open-jaw” ticket (returning from a different city than the one in which you arrived) can be more expensive than a simple return ticket, so also check the price for, say US - London - US and then adding internal flights on one of the low-cost airlines like Ryanair or Vueling, which has a lot of flights to BCN. This would allow you to also enjoy a night or two in one of the Northern cities, which have a totally different vibe to the hotter southern places. London and Amsterdam are especially attractive cities for first-time American tourists as everyone speaks English and they are easy to navigate on public transportation.