The only possible requirement for a training glider the k21 doesn't meet is being spinnable. It's comfortable, max cockpit load is 100kg in both seats, easy to handle on the ground, handles well, terrific in rough conditions and is very, very robust. It also holds its value well. The spin weights are best not mentioned. G is +6.1 -4 and it can be used up to intermediate level aerobatics.
Most pilots that continue flying and get their own glider will eventually own a design of a similar vintage - the discus for example was first built in 1984.
There are two training gliders built in Poland, but they are not that much cheaper and are not as well thought out or as robust. The pw6 dates from 1998 (1st flight) and the perkoz from 2011 but is a 1991 design.
Any glider built in the euro zone is going to be pricey, and if a new design was sketched out tomorrow I suspect the Vikings would be back in the air before it was in production.