tobyo, this is what I see. If you get the flights on the KLM website (MSP-AMS-BCN on the outbound, and MAD-AMS-BCN on the inbound), then the price is about $1140 USD total per person. It looks like with consolidator sites, you can get a fare for about $900 all-in per person, but it would probably involve two stops on the outbound and one stop on the inbound (Iberia and AA). The cheapest price on Delta is $1264 USD total. On Orbitz you can get a combination of Delta and Air France, but again with two stops, for about $1016 per person total.

I'd say forget about the Orbitz prices that disappear. They probably reflect a real price in the database -- for which 0 seats are allotted.

Several questions to consider:
How much are you willing to pay to avoid two stops?
Are your dates at all flexible?
Are your cities at all flexible?

Unfortunately I really have no sense of when you should buy the flight, or what you can reasonably expect the price to be. I just know MSP tends to have high fares, unless you are lucky.

Remember that the seat map chart has no relationship to whether the flight is full or empty, because tickets can be sold without any seats being assigned.

This happens all the time with KLM. Clearly, they have a fare published but Orbitz has trouble seeing that there is no availability. I don't think it is nefarious, but it sure is frustrating.

I am not terribly concerned about the price, it's more the actual flights that I want to book. and it seems every combination that I choose that involves KLM, the same thing happens. I did check KLM's website and the price was much,much higher than I wanted to spend. $1140 is doable so maybe I'll check that out again later.

thanks so much for all the replies and help!

thought I'd post an update to let whoever would like to know, the outcome.

After trying all week to book a few different combinations of flights on Orbitz, cheaptickets, and a few others I can't recall with NO luck whatsoever.....oh wait, there was ONE time that I actually was able to book ONE combination but hubby wanted me to wait to see if we could book the ones we really wanted. never happened. so I ended up giving up and called Delta because I wanted to see if they had discounts for child fares. well....they sure did! but I guess only on certain flights and the one we wanted flying thru AMS to and from would have cost us just over $7000!! um, don't think so!! so, we ended up with flying thru AMS on the way there and JFK on the way home for a much more reasonable rate. but, get this. when the guy was booking our flights HE had issues with one of the KLM flights :D This all ended up taking nearly an hour to complete and he felt bad saying it was Delta's fault it took so long so he issued us each a $50 voucher that we can use only online. Free luggage costs perhaps? anyway, I'm so glad I finally go that done!! and only ending up spending about $600 more than I wanted but prices have gone up in the last 2 weeks so what can you do? I did not want to wait any longer! plus if I take the $150 off of that, I only spent $450 more than I wanted. It's all good.

thanks again for all the responses, really appreciate it!!