I have no serious objections to easyJet (although I would not fly Ryanair or fly in/out of LTN except in an emergency). However, I would be quite concerned about potentially missing your flight if I were you. You have absolutely no protection on your BA flight if easyJet flight was delayed, or you get stuck in traffic, or worse, both, and miss your BA flight.

The roads between LGW and LHR can be horribly congested and can extend your trip time enormously. It can easily take 2.5 hours - two of my recent trips were around the time you are expecting to be driven, and they took that long. I would feel rather nervous about doing that, particularly as you need to clear immigration and collect your bags. LGW non-EU queues are not generally huge, but can still take some time, too. By the time you went through immigration and collected your bags, it may well be an hour or even more after you landed. Bags can be quite slow at LGW. So, you may well only arrive at LHR 4 hours after you have landed at LGW if you are unlucky - now that's 4pm, and after your 'conformance' cut-off (you must have presented yourself at security boarding pass check at least 35 minutes before departure).

It would be very bad for you if you happen to miss your flight, and it would still be quite sad if you lose your opportunity to spend time in the CCR.

Extra $200 each would be a good price for your peace of mind. Remember it includes bags (in fact multiple, as they would let you use your F allowances), and probably a lounge access at BCN, and they are likely to look after you (i.e. rebook you) if your BCN flight is delayed.

With easyJet's $100 fare, it may not include the baggage, they have a one-bag policy for the carry on, and baggage limit is more strict. I really think it would be in your interest to fly BA (or at least Iberia if you must) from BCN.

If you choose to fly easyJet, I would recommend flying in the day before and overnighting at LHR. That way, you should be all OK for your F flight the next day.