Of course, when you are skint, like how I was when I had to build my organ, you may consider building it with a sound module. From what I know, at present there are two good quality modules available in the market, both constituting the self-contained complete stop list of an organ. In the past, I constructed my organ by being fortunate enough to get hold of a 30-note midified pedalboard as well as the bench. All you need to find space to deck up the two keyboards firmly on a table and just plug two ordinary midi keyboards, that are inexpensively available at your local music shops.
For louspeakers, in the past, I bought two sturdy professional Yamaha speakers and used a Volcano subwoofer. Special attention needs to be paid to the speakers because ordinary Hi-fi and other computer speakers shall not be able to withstand the strong bass tones emanating from these organ stops. They will either crack in a terrible way or simply blow them soon. Enquire about a set of Bose speakers, or the similar
professional speakers, preferably with a subwoofer included in the set, to avoid paying extra. To ensure authentic sound production, you need a set which can produce about 25hz-40hz to 22,000hz (22khz) to 24,000hz (24khz).
If you prefer the North German Baroque style, just as I am, you would go for the Content module. In the past, I have enquired about the price of such a product, the Exp-440. Personally I feel it was offered at a very, very economical price, given the number of stops available and the voicing quality. If you are skint, you probably have no other way except building an organ with this module, that gives you 31 stops. It is the best of what you can get in the market for the amount you have to pay. And the module has an interface like an organ stop console. Check out the stop list and other details here:
http://www.contentorgels.nl/product2.aspx?id=190. If you want to hear the voicing, it has been said that the stop samples are from the D4000 series of Content organs. You can hear some demo files of the D4000 here:
http://www.sakralorgelwelt.de/content/klangbeispiele/index.html.
But if you prefer the South German Baroque style, I have also discovered a German digital organ company called Hoffricter, that sells a module that can switch between South German Baroque and alternative Classical/Romantic French styles. But I guess this one is a bit more expensive than the Content EXP-440, from what I can remember from a price list that I have seen sometime ago.
This one gives you 23 stops, with an alternative bank of stops. You can visit this link to see the stop list and hear a demonstration file:
http://www.hoffrichter-kirchenorgel.de/de/Index.htm. After my preview of the music file, I would say it is quite an authentic voicing of the South German Baroque school.
Hoffricter in fact also sells a six-stop module for one manual and the pedalboard. If you just want to practice on one manual and the pedalling skill, this one may be an option. See the stop list and the alternative bank of stops here:
http://www.hoffrichter-kirchenorgel.de/de/Index.htm, and hear the demonstration file.