There may not always be an opening for a new unit. Contact the league administrators for more information. SL is supported by sponsorships, so there is no cost to the playing public. Corporate costs would depend on what level of intergration was required and the nature of the product involved. SL only supports full versions of the software.
Demo versions are generally too limited in scope to justify the effort required to run a league.
As well, SL tries to maintain a good relationship with the game developers. Supporting free demos would jeopardize that relationship. From time to time SL may run a beta gameplay cycle of a league using demo software. Such beta cycles end at or very shortly after the release of the commercial software and are only used to refine development of the forthcoming league. At SL all the staff are gamers.