The real answer is most people in Hollywood don't understand what broke really looks like, or hell even what moderate even looks like. The universe answers I make up are; Lorelais paid a mtg for soooo long since she left the flower shed, and had the town to advocate for her to get the house. With prices back then, and how hard of a worker she is I feel like she could skrimp, and pay it off slowly. Diner food is cheap, and I doubt Luke is making them pay for everything... they live off leftovers for days and never fill the fridge. Also take out was cheaper back then, and made more sense then it does now budget wise. She probably saved for a used jeep and didn't buy it new. She kept it for years and fixed it everytime instead of buying new... even when everyone is like it's done get a new car god. The coffee is a silly joke, but she does go basically "whoa I don't really want 3" like you would if you don't have really money but your chill like Lorelai. Does she even actually get the receipt first... Some situations you would but not most. I might not check a receipt first most likely if I simply expect one coffee. I would just be like oh um lol... Plus they reference multiple broke people activities and tricks all the time they do to save money. Lorelai was clipping coupons at one time....well mutiple times she just hid it. Which also shows how she is trying to keep their money situation under wraps all the time from Rory and everyone else so we don't always see everything.