The other day, a friend and I were in Babies R' Us, looking at how much regular disposable diapers cost. Then I found biodegradable inserts and covers. They were made by gdiapers. Now, I am fully on board with cloth, but I had to check these "hybrid" diapers out. They are similar to pre-folds because you buy tons of inserts and a good amount of covers. The gdiapers covers are $16.99 for one, and they come in specific sizes. They are slightly adjustable around the waist, but it is most like a diaper cover or a perfect size diaper - you have to buy multiple sizes to go from newborn to potty-trained.
Then you have the biodegradable inserts. They are very appealing because you can flush them, but they are not appealing to the wallet. One bulk size of 128 medium inserts costs $52. If a baby needs to be changed 10x/day, then a box of these refills will last approximately 13 days. Therefore, you would need about 2 packages to get through each month, spending over $100 PER MONTH on just the refills! Not to mention buying about 20-30 covers before they are potty trained.
If your main concern is being earth-friendly, then by all means, use this style of diaper over the typical disposable. But, if you are looking to be earth-friendly AND cost efficient, this isn't the best option.
gdiapers covers and refills
GroVia is another brand that makes hybrid/biodegradable liners. Their costs are almost exactly the same.