The sintratec s1 currently retails at over ?20,000 in the uk.
Not sure how that is either low cost or within the budget.

The build it yourself kit is 5,000 euros.
That's not a bad price.

Bear in mind with a 'budget' nylon sls printer. There is an awful lot of post processing: powder handling, print finishing and polishing etc
Also you really don't wnat to be breathing in the powder - which is pretty expensive compared to fdm filaments.

All that being said - yes an sls machine is kind of essential for a print bureau these days.

As far as fdm machines go - ultimaker don't give good value for money.
The prusa mk3 is probably one of the best kits around and you almost never hear anyone saying anything negative about them.

The form 2 is a good option.
Yes the resins are expensive - But if you're looking at retail value then custom figurines for gamers and custom parts for cos-players are where the best market is currently.
Also bear in mind that printing at a machine shighest quality settings is never really that practical.
A faster lower quality print and a couple of minutes post processing with some fine grit sanding cloth, is usually a better option.

If you want volume and speed and quality - have a look at the formbot range of printers: http://www.formbot3d.com/formbot-big...ize_p0017.html

The independant dual extruders make printing non-optimised designs much easier.

The biggest problem you face is educating the average-person-in-the-street.
Explaining that 3d printing is NOT injection moulding.
Making money out of it is pretty much dependant on finding a niche that nobody has yet filled and producing unique or custom objects with a high per item value.

Because of the time and cost of mass producing cheap items - you will never be able to compete with existing injection moulded products. So don't try.

So before you buy any printers - you first need to identify your market and product(s) and then look for the best solution to make it/them.