As much as I hate the way it played out I'd say that the 2600 Star Castle Kickstarter example is a way to do this that you might not have considered. You can set a money goal that can, if you feel like it, include development costs. You don't reach the goal, you don't move on it but it would seem that people would expect something soon so you'd almost have to have been working on the game before getting the money. But you could set up pricing and availability that way that would for sure cover your costs. What I didn't like about the Star Castle example was that the guy got waaay more money than he was asking for but didn't allow for extra carts to be made for purchase. So someone like say, me, who didn't hear about it until a week later, was S.O.L. in terms of getting one even though the guy got plenty of money to produce a few extras and I would have put down for the boxed (most expensive) version. I wouldn't do it that way if you went that route, I'd allow for some of the extra money to either have more examples made or get folded into the next game down the line.
I would like to see a Vectrex Kickstarter with tiered pricing for cart only, cart + manual and cart + manual + box + overlay. Since boxes and overlays are the biggest pains they'd make that 3rd level the most expensive. It would be obvious how many of each were being asked for and the pricing would cover that + maybe some extra for the effort. If it exceeded the total then some extras could be made for after-the-fact sales. Maybe after 2 or 3 of those you make a name for yourself and don't need Kickstarter anymore.
Also, pricing depends on what you're making. If it's a popular "Why wasn't this game ever made for the [fill in the blank]?" port then you could probably charge more than for your own unique idea that might not resonate with potential customers. I'm thinking of a Halo or Boulder Dash for the 2600 or a Warrior for the Vectrex or a Moon Cresta for the 7800 as opposed to a game that might be really cool but nobody can wrap his head around your description, you'd have to already have them made so people could see a YouTube video of gameplay or something. Along with that, if you go the full monty with boxes and screen overlays (Vectrex) or controller overlays (5200, Intellivision) then you could charge more for that "completeness" as well.
There's also the possibility of teaming with others who already exist. Marc on this forum offers boxes for some games (which I've bought and really like), maybe he could be convinced to make them separately for your games and whoever bought your carts would be told to contact him for any box needs. And omeganu makes overlays for Vectrex games that are pretty good compared to the originals and he also makes overlays for homebrew games that never had them, you could supply him with the image and be done with it from your end. Actually I hope more homebrew programmers do that, I think it's best when you can have the option of compiling a complete homebrew game as opposed to just having a downloaded file to run on an emulator.