The problem with big box store planes or cheap planes in general is that the mating surfaces between the frog and the sole are often not machined at all, just raw castings. These will never really be capable of doing fine work unless you happen to be a machinist with some time on your hands.
If you’re not comfortable buying from ebay, there are some reputable used tool sellers online that will give honest descriptions of the tools they are selling. These tools will be a bit more expensive (but not always) than eBay but much cheaper than a new premium plane. I have bought a number of items from Josh at hyperkitten.com. If you email and tell him what you are looking for, he can probably find you a solid user plane at a reasonable price. Or maybe one that is a good candidate for refurbishing for less money.