Unfortunately, you're in dream land there mate.
Firstly, you're right that Brentford are a "selling club", but the market for their players are premier league clubs and the wealthiest championship clubs - we're neither yet.
Secondly, you say the fees aren't "rediculous" - this season Jota went for £6m and last year they sold Hogan for £10m. Based on our incomings to date, that's obviously out of our budget.
Finally, on to his wages, and this is where I think you're furthest from reality.
He signed a contract extension while in the championship, with an established championship club - it wouldn't be unreasonable to assume he's on championship wages. We wouldn't just have to match that: he's not going to uproot and move from (desirable) London to the (much misunderstood) Sheffield without a considerable wage hike.
Assuming that our players are on upper L1 and lower Champ wages, he would likely be our highest paid player (probably by some margin) and I'm certain that wouldn't be a good move for team spirit.