If you're set on getting a display tablet, you can get one for a lot cheaper if you buy from ebay. Huion has a page where they sell refurbished products that are pretty good quality.
That being said, I really think you just need to practice a lot more with the tablet you do have. Hand eye coordination is different for everyone, so it's okay if you're having trouble getting the hang of it, you just have to get some practice. Try drawing simple shapes to get a feel for it.
Personally, I started out using a track pad ages ago, then I got a Huion HS64 some years back. It's a pen tablet and it took some getting used to, but all my covers and art until recently were done with it. A couple months ago I got a Kamvas pro 13 and there wasn't much of a change. My lines are more precise and truer to what I draw with pen and paper, but the biggest change--and the main reason I bothered to upgrade--is that I can draw faster. As far as skills, you probably won't see too big a change than if you were to just practice with the pen tablet.
If you want to wait and save though, you could at least keep working on your comic and sketching out pages so you have something to work with when you have your display tablet. It'll make it faster for you to build up a backlog then. Either way, I'm glad you're not going with AI. It's really not worth it for the trouble it might give you later on.