you may want to check out my answer to http://forum.3ders.org/showthread.php?tid=161
That sounds like a really interesting application, if you are willing to share some info, I'd be interested.
Most cheap printers have a smaller print area, what would be the minimum? You can also glue things or turn them 45 degree to fit them on smaller build areas, that is how I do it.
As for your "wish-list":
1- Both reprap based printers and the open source software have evolved into great products. With enough tinkering the quality can match commercial devices.
If you are looking for something tinker-free, I can recommend the UP from PP3DP, but it may not suit your requirements (works best with ABS and has a smaller print area then some printers). But the quality is great.
2- Print with PLA. Other then with ABS there is little to none warping. PLA does get soft at lower temperatures though, so it also depends where you are using the parts. If used in an environment where it gets over 70 degree Celsius such as motor holders it may result in problems.
3- Most printers are able to print hollow, even the UP now in the latest software version. Before that Reprap could do that without problems. There you also have the advantage of automatically letting the print pause when reaching a certain point, but you may have to create a script to do that (not aware of what programs can do that atm).
Other then pause the print and insert something it is often easier to create half-parts and glue them together. Sometimes a lot easier, especially if you make a lid you can remove for testing and then glue it shut when everything is working a 100%...
4- This is a bit of a point-of-view thing. Of course you can buy most printers assembled, but it is helpfull if you build one yourself so you are able to understand and repair it. Then it's easy to use :-) Also it has the benefit of repairing it yourself. For a commercial printer like the UP or bigger commercial printers you will have to pay for replacement parts and/or get a service contract...
Soft- and Hardware need to be set up perfectly, and sometimes you have to change things for every print. Sure, it can be learnt, but keep in mind that it takes up quite some amount of work-time to find the right settings for a new part, especially the first months you own your printer, and then again when buying new plastic from a different vendor or production line... Probably one reason the UP is so easy if you keep buying the OEM material, but it costs two to three times as cheap no-name plastic...
Here is a comparison of the settings you have to make,
Slic3r (open source, for reprap printers)
PP3DP UP's software
While it is easier, it limits your tuning possibilities... though in 98 out of 100 prints the defaults will do :-)
What kind of parts do you want to print?
Please share an example of what kind of quality you had in mind. It will help to recommend a suitable printer. As for the technology (SLA, SLS, FDM/FFF) read the topic in my first link, I tried to summarize some up- and downsides of the different methods.
In general FDM/FFF/Extrusion is a rather clean, hassle-free and cheap&fast solution, while powderprinting/SLS has advantages when printing a higher number of parts.
If you print a single part on a SLS printer it will take long and waste lots of material.
Even under 1000£/ €/$ there are great devices available.
Also check out the Make 3D printer buyer's guide