Well to each their own. And their budget.
The same goes for people who pay a tshirt 10$, 100$ or 1000$.
People paying a T-shirt 10$ and 100$ might think the one paying it 1000$ is crazy.
Same for the one paying a tshirt 1000$ might think that a 10$ or 100$ is not worth it.
There is both bad or wrong. Just something fine and fitting for each of us.
You're just telling him how he should and what's best to use his money which is intrusive and performative.
No, I say this as someone who knows what he's talking about. As I said, I've done this more than a few times. What people fail to realize are some of the hidden costs involved in these excursions, both financial, personal and opportunity costs. In order to be reasonable you need to consider properly feeding your companion, and I don't mean hot dogs and fries for a week. You need to consider entertainment and drinks. You need to consider airfare, shopping and large variety of small incidentals that add up. You also need to consider what happens when you find that after a day you no longer enjoy the company of the person you're with, and that your interests and goals for the trip are entirely different. When you want to send them home early what is "fair"? Or do you suffer through the rest of your time? What do you do together when you're not in bed? Do you have to give up activities you want to pursue in order to accommodate? What about food choices? Do you try to establish "dominion" over her company or is she a free agent and what is your expectation for time together? In an area where there is opportunity do either you or she have free reign to see other people? There's aa zillion little factors that go into this. The money is just a piece of it.
Now, having said that the destination of the trip is important because it dictates whether there is ample opportunity (sand to the beach) to meet other ladies locally or whether you're going somewhere where that isn't a possibility. There is a philosophical question involved here in whether it is even worthwhile to consider this when you could date someone locally in their own country for a week or whatever without having to do any of this stuff and also have an easy escape hatch.
As for cost, there's no question that it's considerably more expensive to take someone with you. By a huge margin. Not everyone has that huge margin to play with so yes, I'm telling him that the obvious option isn't the only one out there. Or necessarily the easiest or the best. There's a number of factors to consider.
I never said I ever paid $10k for a 4-5 days trip

But in my opinion it’s likely the budget if you want to go somewhere really nice with the top SPs from here. Montreal
Or just choose to stay in Montreal and enjoy making 30 to 35h of booking whenever with whoever with the same budget
I don't disagree that what you propose is a likely budget for what you propose. There's a couple of things to bear in mind. Not all MERB members in this discussion are from Montreal, so there may be added factors and costs associated with it that may make it practical to take someone from their own home town instead. Secondly, 30-35 hours of fun really isn't much. On the budget you propose you can (and I have) literally bang porn stars and models in other places for a week for that much money and come home with change. Or you could go to Asia, say the Philippines for example, and monger for a month including all stays and meals and drinks, with an afternoon massage every day and banging a couple of times a day easily for the budget you propose.
I'm not saying that these are necessarily better options for you or anyone else. What I am saying is that unless you have a close personal tie and level of trust and desire in the person you are proposing to take that you owe it to yourself to at least consider other available options.