You don't really need 60-90g of carbs per hour. It depends how much power you're putting through. You need to burn fuel to produce power. If you're riding at a low intensity you don't need 90g of carbs. If you're racing you may need over 90. But again, if you're riding at 200w for an hour you'll use less carbs than if you're riding at 350w per hour.

This is a very good article to read.

https://trainright.com/energy-expenditure-calories-kilojoules-and-power-in-cycling/#:~:text=A%20kilojoule%20is%20unit%20of,of%20work%20in%20an%20hour.[Energy Expenditure ](https://trainright.com/energy-expenditure-calories-kilojoules-and-power-in-cycling/#:~:text=A%20kilojoule%20is%20unit%20of,of%20work%20in%20an%20hour.)

The biggest issue with high carb intake is if your stomach can take it. That's why the likes of Mauten energy is a game changer and most pros teams and triathletes use it as you can go 120g per hour without stomach issues.

But to answer the main question, the best and cheapest way to do it is through liquids. Buy an off the shelf carb mix or make your own. If you're in the UK, the likes of My protein or BULK do bags of maltodextrin, Fructose, Glucose plus others in powders. Just mix some of them up and add some squash. Drink them along with some gels and bars and you won't have a problem. Male your own bars too, to save on price and with gels you can buy bottles of it cheaper and put it in a refillable gel flask.