Let's be honest - if it wasn't an informal setting among friends and he was actually pitching a business idea to investors he wouldn't get away with talking for so long. If this was The Apprentice or Dragon's Den he'd get cut off mid-flow.
Although you clearly respect your friend's right to speak and don't want to offend him, actually in this informal setting you probably have a lot more leeway to speak frankly without causing offence than you would if it was formal.
To encourage him to get the point and bring the subject to a conclusion, I would try this approach - interrupt him at an appropriate point, but stay on the subject. You're cutting him off, but you're not shutting him down.
This sales pitch is a bit long. You'd never get anyone to invest with a drawn-out pitch like this. Let's break this down. Your business idea is to buy things cheaply direct from China, then resell them at a profit on sites like Amazon?
This shows (i) that you have been listening to him because you have been able to summarise his pitch, and (ii) that you are interested in it because your criticism is constructive and you want to make it better.
See how he responds. Hopefully what he says from here on will be shorter and to the point, and the subject will soon be exhausted. It may be that he was meandering and repeating himself because you were just letting him speak openly without interruption.
Interrupting someone isn't always rude. Sometimes people just talk and talk until they get something back from the other party. Look for them pausing, slowing down, or sending non-verbal signals that they have exhausted what they want to say. But even if you don't get any of those signals, when someone has dominated the conversation for long enough it is fair to interrupt.
If this approach doesn't shorten his pitch and bring the subject to a conclusion, then you could say:
Well I am interested in what you have to say, but I don't want to talk about business all night.
Either invite him to "wrap things up" if he still has something left to say and you don't want to offend him, or feel free to call time on it and change the subject if you've had enough. Being honest with him is better than just seeing less of him, because at least he has the choice to modify the behaviour that is getting you down.