but for the necessity to send invites; this gets problematical with classes of 28, sometimes several in a term :(

Actually, DW will happily make a "promo" code for anyone who wants to bring a group of people over -- it's a single code that allows multiple people to create accounts.

If you want one, just e-mail accounts@dreamwidth.org or open a Support request in the Account Payments category. Should be no problem at all.