I've seen £79 million bandied about a lot consistently for a good few weeks as the cost to prise Dembele away from Dortmund and from what I've seen of him I don't think we'd sell for a loss if we sold him on later down the line.
It's known he loves Barca but right now they're not in a position to buy him as they've clearly prioritised right back, centre back, central midfield and Deulofeu for where they desperately want to strengthen and I've seen in a lot of places the majority of their budget is for Bellerin and either Verratti or Saul Niguez.
I think it's very clear right wing/forward is a priority position to strengthen as neither Mkhitaryan or Mata are at their best there whilst Lingard and Rashford (if he plays wide) are better from the left whilst Martial is also there on the left so unless it's an upgrade like Alexis Sanchez there's zero point in a left winger/forward.
Reality is Dortmund won't want to sell BUT they ARE a selling club IF the price is right and they could probably stretch us to £80-£85 million which would allow them to strengthen their entire squad and push Bayern a lot harder than last season, Dortmund are amazing at quietly unearthing great players then selling them on and I think they'd have a plan in place in the event Dembele was sold because they're very efficient.
A front 3 or 4 made up of Dembele, Morata, Mkhitaryan, Rashford, Mata and Martial with Lingard and (sigh) Rooney as final options is a lot more varied and balanced than last season and I believe we'd be better going forward and converting chances into goals with this potential group than last season too.
Dembele would allow Mkhitaryan and Mata to play more games as a 10 when we play 4-2-3-1 and give us natural balance, pace and width and the space created through the middle from having natural wide players could allow Pogba to rampage through midfield especially with a new out and out defensive midfielder signed to release the shackles.