Saliba to Real Madrid would definitely be great, but even with all the money and convincing in the world, Arsenal would try their best to not sell him. The problem sometimes isn't the money, it's the valuation. Imagine you have a player who is actually worth 50 million, you know he worths just that much, you know he doesn't worth 100, but for your team, the club values him at 100 because that is how important he is to the team, from chemistry to setting to leadership to many other reasons.
Arsenal has confirmed it many times. Saliba is not for sale.
I think all football teams apply such rule. They were pricing their players based on how important their players for their club. Although these players have low market value. But, I don't know what metrics determine a player's market value. And I assume that parties have different metrics. Then, I think the club always values their player highly after he makes a big contribution. The player's contribution is a parameter for the club to value his player highly or lowly.
So, why would any other team pay 100 to a player that worths 50? They wouldn't. This is the same logic, Saliba worths more to Arsenal than what he is actually worth, and that is why I do not think that Real would be able to buy him, they will have to wait for him to finish his contract.
But i think that logic may not be applicable if the player itself requested the club to sell him. Real couldn't buy Saliba. It's not due to money, but because Arsenal still needs him as a defender. The only choice for real madrid to pursue Saliba directly.
It may be working consider saliba can push arsenal to let him leave to join real madrid.