You have spoken mostly about the price. You have also talked a bit about the capabilities. You are thinking it would be nice to have a bigger mill.
Bigger is not always better, however in the home / hobby market, the ones that most people refer to as "big" machines would be considered "small" in the majority of commercial / industrial environments.
I encourage you to focus on what it is you want the milling machine for and look at what your constraints are (such as room, power, transport and any hard stop on price). Of course the cost of the machine matters, but I suggest you put that criteria well down the list. Strictly speaking on a machine that you will have for many years, that will be the cause of you spending a whole lot of additional dollars on setting it up and tooling it - the initial cost of the machine (even a full price new one) is still one of the lesser costs. It is much cheaper to spend the extra money in the beginning to get a machine that will do what you need & want than to struggle away with a lesser machine, get frustrated, go and purchase another machine etc.
You will come out ahead if you spend extra on the basic machine, than if you go cheap on the machine and don't get features that are difficult to do without.
What size? Your work envelop gets eaten up very quickly. That is one of the big drawbacks of the lathe/mill combos - the effective work space is very small. Regardless of the machine, by the time you mount a vise, then add a collet chuck (or drill chuck), then you put a tool in that chuck - you just lost about 6" of your head room. I have two mills - the smaller one has a work envelop of 12" x 8" x 12" (X-Y-Z), it is an extremely versatile, unusual little toolroom mill - I really like it, but since I got a regular knee mill with 10 x 48 table (28" x 10" x 17" - with additional "Y" on top of the knee to augment the 10" of travel), I hardly use the smaller one.
The knee mill that "Bear" posted a picture of above is a very nice, useful size, small milling machine. It is a great size for general mucking around, this and that sort of work. That is a "small" mill and super handy. It is easy to power (probably 3 HP), it is not real heavy (perhaps #2500), easy to move with rollers, jack, floor jack and it has a very respectable work envelop.
If you know that the stuff you are working on is all pretty small then a bench mill might really work for you - obviously only you can answer that. I encourage you to focus on the capabilities and not focus too much on the price. Pretty quick the price is forgotten. If you end up with something that doesn't work for you, then you will always be reminded that you wasted your money (regardless of how cheap it was).
Let us know how you make out. David