Not exactly to get enrolled, but in Moscow websites officially advertize 2300000 rub to sign, which is about $25000. Then monthly payment is 190000 rub so for first year it'll be about $50000 which is 5 to 10 times more than average salary (depending on the region). Initial bonus for enrollment is city-dependent but as far as I understand anyone can just travel to Moscow and sign in there.

I heard that volonteer numbers right now are pretty high so army became more selective - people expect that war will end soon and hope to get sign in bonus without spending much time on the battlefield, if any.