Here's the promised continuation of who I would expect to actually go out and colonize other planets. Well, wait. I lied. First, I want to show my reasoning for my thinking, and then I'll actually talk about the colonists. Procrastination!
Let's work backwards. The way I've deliberately set the systems up, once you pass through the gate to the stars as a colonist, you're not really coming back. This means both that you leave anything you can't bring with the keepers at the gate, and that you can't sell much of anything to someone who hasn't entered the gate. While all this includes family heirlooms you'd want to bring but can't, it also includes money and precludes you from getting loans as there's no possibility for you to pay them off once you've entered. If you want to enter that gate, you need to pay the gatekeeper his fee, and pay it upfront.
How expensive is the gatekeeper's fee? I'd think pretty expensive. In this setting, I'd assume that much of the actual fee would be helped by side effects from having the fleet and infrastructure anyway, but it'd still be expensive. If I had to guess, I'd put it at least one million dollars to start before any side effects, with the price dropping off as research and familiarity with the subject increases. But I wouldn't be surprised if the cost were higher; the scale of these projects can get away from me sometimes, especially when there's few good analogies in the present day. I can use cost to orbit, for example (~$10,000/kg) as a reasonable cost, but it'll always have accuracy problems. Military deployment calculations are also useful, due to similarity at times where one is attempting to get materials and personnel to locations without the proper infrastructure for it, but the lack of good transportation parallels still makes it odd. Good to read for learning about random things one might not have thought about.
But I digress. Calling it expensive is enough for this exercise, I think. I don't plan on using real numbers anyway in the game precisely to avoid these sort of issues. (Think of X-COM's credits as an example) It's expensive enough that only rich people will be able to afford a ticket straight up. Anyone middle class could put in a sizable dent, but certainly not enough. For most people, they're going to need a sponsor of some sort that can help pay.
Historically, the sponsors for colonies were often rich men looking to profit, viewed it as some variety of charity, or were looking to go there themselves. Unfortunately for people in this setting, I'd be surprised if there was much funding from those hoping to make a profit, as no goods can be sent home. I'd imagine some company with too much money might try it as an advertisement stunt (Facebookopolis!) but I wouldn't get my hopes up. I'd also be surprised if there were many willing to go themselves. That brand seems more the type to participate in the administration, then settle down on a colony later, rather than becoming an outright colonist.
However, the availability of charity seems quite likely to be a good sponsor. Especially nowadays, there's no requirement that it be just one sponsor, but that general funds could exist. Along with charity, they'd have a major advantage in funding over their historical counterparts with the large expansion of the state. State subsidies for colonists seem likely, and possibly plentiful as states compete with one another. For the setting, I'd think the interesting point would be less gaining state funding, but intentionally limiting it to make things more interesting. State colonies that are extensions of their Earth counterparts would work, but would also break a personal rule of the setting that space colonization is seen as a deliberate side show, and dissociated with the governments themselves, leading to the outcome where the costs are borne by the player, but effectively subsidized by the budget from the combination of all nations.
Which leads to the final question: who actually goes? Historically, it seems that the vast majority did so in order to flee something from the old world. Well known sources of fear were religious persecution and war, but also more mundane fears like economic hardship. Along with those who chose to go, some were also sent. Prisoners and debters were common, along with the occasional man effectively exiled for political reasons. I'd think that much of these would certainly apply today, dependent on availability of volunteers. Sending prisoners isn't a very good option if there's already a flood looking to leave, but if you're having troubles finding people to go, giving prisoners the option of going doesn't seem like a bad idea, especially for the less popular destinations. (I'm assuming that such prisoners would have at least some restrictions based off of their reason for incarceration. In the long run, it's likely to be quite a bit cheaper)
What does all this mean for the player? I'm not really sure yet. It does provide me a lot of room to experiment with to see what works best though. All that I've said here allows for more information and possible game restrictions for the player player to deal with, but I'd be lying if I didn't think a lot of it was unnecessary and possibly unwanted. For example, does it matter why the colonists left Earth? It could affect stats or place restrictions on which colonies they could end up in, if I were interested in showing that. Could be pure fluff, if I don't want to simulate it to such detail too. Should be fun exploring though, to see which works best, and how far it gets before it becomes just noise.