I'm surprised no one has said "I'm in debt up to my neck" as I suspect that is a common way of doing this stuff! :D Financed cars, credit for fuel, etc.... ;)
(As accurate as the above statement may seem for some I say it in jest knowing full well that's not the best way to do it!)
For most stuff, our budget determines our travel goal, not the other way around. Our biggest variable cost is our fuel. We know our fuel calculations are not too far off when we say we will use 20 liters/100 kilometres (Jeep gets 14, Bike gets 4.5, that combined is 18.5 so the 20 L/100 gives us a budget buffer). We get an average price for our route by gas buddy and usually increase it by 10-15%. Our food costs are pretty static no matter where we are. The nature of my wife's work means when we travel there's an opportunity cost as well (she is paid hourly and thus, time off = no pay). So we calculate all that stuff together in terms of our available resources, and then we decide where we can afford to go. Some bucket list items means we save year after year to make 'em work, but most of our trips are dictated by dollars.
In terms of where our rigs are at, we do a lot of home-made solutions and we do all of our own maintenance that cut our costs down and frees up some income to go to our trips. When we have to purchase, we try to wait for group buys or sales or if possible we buy used. Sometimes, though, we have to pay full retail.
There's only two ways to increase your expedition funds -- make more money, or spend less money on other things. We try for the first but obviously that can be outside our control, so instead we focus on the second. We currently live in a really cheap house in a rougher part of town that keeps our mortgage payments low. It's simple, but we are comfy and happy. We use coupons and buy in bulk and plan our weekly groceries out week-by-week to try to keep that low and do one shop instead of 3 or 4 -- those little purchases add up. Most folks I speak to who "wish they could get into it but don't have the money" actually DO have the money, they just choose to spend it elsewhere -- which is totally fine! Just different priorities.
If a person gets a household budget application like Mint or You Need A Budget and gets a handle on where their money is going every month, they may be in a better position to afford some stuff. We used to really enjoy wine, but a bottle of wine a few times a week (Say, $15 per bottle twice a week) works out to $1560/year. That's enough cash based on my napkin math to ride my bike to Tuktoyuktuk and back three times! Another $500, and we'd be able to do a bike-and-jeep trip. But its easy to spend the $15 bucks on a Friday and again on a Saturday, or buy that lunch at work twice a week because I 'forgot' to bring one from home. We used to be a bit like goldfish when it comes to their finances -- We grow to fill the space we're given.
Adventure doesn't need to be expensive, even though I get that this is a trend in the vehicle-dependent-travel community. For folks who can afford the $110,000 for a tricked out defender and another $25,000 for the tent, fridge, alu-cab, and Expo-cool trinkets and farkles, more power to them and I'm so glad they have those resources. But give me just $10,000 and I'll buy a brand new KLR 650 and travel around the world with spare change left over. If I shop used, I could do it for far less. If I recall, this is a challenge Scott Brady wrote about a few years ago. A person can do a lot of adventuring with a lot less money, it just might mean changing the attitude. Do you need the $400 integrated tailgate table when you can get a plastic one from Costco for $50? Do you really need a table at all, or can you make due cooking on your fender or hood? Your money, your choice, but I would never let the desire for a better piece of gear get in the way of doing something cool. It just might change the cool thing a little bit.
And to be clear -- we far and away do NOT have this all figured out and we are constantly making mistakes with our budget. The above is an example of a different way of thinking on funding these trips. Don't worry about making more money -- worry about spending less.
Edit: Actually, worry about both. But not TOO much. Worry is like a rocking chair after all -- gives you something to do at the end of the day you're still just sitting there!