200 rounds a week on a Dillon 550 is about half an hour or maybe a little more depending on if you are including filling primer tubes, powder measure, and getting components ready. They say it is a "400-600" round per hour machine. I have never done 600 on mine in an hour, but I have done over 500. For major matches or when I am making "best quality" handgun ammo, it is probably somewhere around 350 - 400 per hour but I am taking my time. If someone else was keeping the machine and bins stocked with components, 600 would be reachable.
Like ftsibley, the Dillon 550 was my first press. I personally think it is fine to start with a progressive. Just because a machine can load fast doesn't mean you have to start wide open, and if you know you want 200 rounds per week, well, a singlestage wouldn't be the way I would want to go. The 550 is very simple for a progressive and easy to learn on. Some will say the 550 is "bad" because it is manually indexing. However, I think this can be good, especially for someone new, as automatic indexing could be more confusing when or if something goes wrong. The manual indexing just requires your attention and a habitual motion. The right hand sets a case, pulls the handle, pushes forward, then the left hand rotates the shell plate and sets a bullet. Repeat every cycle.
I know some very good tactical rifle competitors that load long range rifle ammunition on Dillon 550's and 650's. For optimum match accuracy, I believe they are weighing powder charges which slows down the rate of production by a good bit, but all of the other operations are done on the progressive press, and they load some of their practice ammunition with the Dillon powder measures at regular production rates and say the accuracy difference isn't much.
The 550 is also VERY easy to switch calibers and is the easiest of the Dillon presses by a little bit. If you are staying with the same primer size, you can switch calibers in 5 minutes or less. If the case head is close enough in size that the shellplate does not have to be changed, it is more like 1 minute for a caliber change. Swapping primer size does add probably 10-15 minutes to the conversion. BigMike or Captain, if you are ever down in the Hattiesburg area, you are both welcome to come by and take a look at my setups.
Used Dillon machines do become available from time to time, but they usually don't stay on the market long. There is some savings involved, but they hold their value reasonably well. Typically it will be a Square Deal or 550 because someone is moving up to a 650 or 1050. I was fortunate to grab a used Super 1050 that a friend sold when he got out of competition shooting for less than half of what a new one costs today (there have been a few price increases since then though). It is the only press that doesn't have Dillon's no b.s. warranty because it is considered a small batch commercial press, but I haven't needed anything for it in over 6 years other than the plastic bottom of a primer feeding tube, and Dillon sent one to me for free anyway even though I told them it was for the 1050 and not the 550. I just loaded right at 500 rounds for the MS Classic on it in about 25 minutes, and that includes having to fill the case feeder, bullet feeder, and powder hopper. It is a good bit more complicated than a 550, but it's nothing ridiculous. It is of course more involved to switch calibers too, but I leave it setup in the caliber I shoot most (.40S&W) and load everything else on the 550.
I've never owned a square deal and I only owned a 650 for about 10 minutes (won it at a match and sold it to a guy standing next to me), but I have loaded on both and can give you my thoughts, for what they're worth, on them if you're interested. Dillon also has interactive purchasing guides for their machines here: http://www.dillonprecision.com/customize-reloader.html
I'm sure vranasaurus would give you an honest opinion on the RCBS Pro 2000 he is selling. He has already said he is selling it because he is moving up to a Dillon 650, but I think the Pro 2000 compares with a 550 but does have automatic indexing and a 5th station. I have never been around one of them though, just heard some good things.