In the tropics I am happy with anything that covers my skin and fits. I have used lycra skins, which are cheap and comfortable, but aren't very durable. Unless you're really oddly shaped, you can easily get a well-fitting lycra suit. I used to use a neutrally buoyant Polartec suit, which wore out on me; it was not particularly cheap but I will get another one as soon as I see one on a store's rack--that was my favorite wetsuit. Right now I use a Henderson Hyper-stretch, which will fit most people off the rack and cost me about $150, if I recall correctly. As an aside, I have to commend Henderson for taking Scuba marketing to its logical conclusion by including "titanium" in the name of many of their neoprene suits and raising the price accordingly, without going through the charade of adding actual titanium.
Since you are considering a 5mm suit, you are either more susceptible to cold than me or contemplating diving in colder water than I ever encounter. In my experience, as suits get thicker fit matters even more, and it becomes harder to get comfort cheaply. My 5mm is an off-the-rack Henderson and is reasonably comfortable, but my 7mm--which I long since abandoned to a scrap heap--was custom made and, in my opinion, well worth the money. Not because it was of superior quality--although it may have been--but because I could not have gotten an off-the-rack suit that fit nearly as well.