At that price point it is likely whatever you buy is going to need some work to make it work. As others have said, avoid cheap planes, yes you can buy more for the same money but everyone will be a paperweight and mock you when you look at it. the Stanley premium no 4 looks alright to me but it is almost certainly going to need work to work well.
I'd go with an early Stanley used personally. It's a bit daunting sifting through but it's easy to work out when you know which features to look out for and which questions to ask. Plenty of sites to have a read through, try Hyperkitten and Patrick Leach's Blood and Gore. Blood and Gore in particular is just a good read on it's own if you have an interest in wood working tools anyhow. You can generally get some rough idea of age based on simple visible aspects such as patent dates behind the frog, made in USA text, the type of lever cap, dates on the plane blade, etc. The low knob versions fetch the higher money but you can get some bargains sometimes. These are generally type 11 and earlier (up to 1918). You will get low knobs (indeed most hardware) on different planes sometimes when people have changed them over but this is rare and unlikely to be an issue. Anything pre-WWII should have a decent amount of iron to the casting and made to reasonable quality. The Type 17's (1942-45) are a bit of a sweet spot as the castings are just fantastically thick and they are at the end of that spectrum.
I would say that given your requirement to level and smooth, you will be better served with two planes. The size of the wood you are working with will dictate which size is best. The bigger the surface area the larger the plane effectively. Tabletops will be easier to level with a no 7 or a no 8, although a no 6 would probably do the job but these seem to be fetching higher money these days.
A 5 1/2 would also work in levelling table surfaces, it will just require more work to achieve the same result. In terms of a smoother a no 4 or 4.5 are the more practical, no 3's are lovely and one of my faves but again, higher money. Don't go for the shiny ones all freshly painted, they are often hiding something or have been abused in the process of making them shiny in the first place. There is something to be said for an honestly well used plane. Broken or chipped totes shouldn't be an issue either - easy to fix as long as the metal hardware is all good. Make sure the metal sole is intact with no cracks or fissures. Make sure the mouth is sound with no chips around it and that the width is not too wide (people will sometimes file it larger to remove chips). If you can get a frog with a solid metal face as opposed to the milled version (google it, it will make sense) this is better in my opinion but not a show stopper. Surface rust is easily fixed, chances are you're going to be flattening it at some point anyhow. Avoid however any bad pitting, you just don't need the hassle and there are enough planes about for this to be considered an option.. The Made in USA planes are usually not a bad buy either.
I would plumb for a pre war no 4 and no 5 1/2 combo or a no 4 1/2 and no 7 combo. Either way I would also factor in a block plane when you can as well.
The boutique dealers are a good start and probably the best bet however this will up your budget. They have taken the initial risk, cleaned it up, likely sharpened the blade and adding their rep to the sale. That comes at cost and rightly so. Also factor in sharpening into the equation if you don't already have other edge tools that require that. Plenty of decent diamond plates and water stone combinations around so this shouldn't be a problem. Don't ask a forum the best option to sharpen an edge unless you are well stocked up on popcorn.
