Maybe guild which had low amount of total players in it during last boot
should give discount from guild levels. This might make these guild bit more
favourable to reinc in. Also, this feature might need to be disabled for those
guild which need player invite to join in.
How big this discount should be and what is the limit for discount to begin
is might need some observation and statistics to be made.

An alternative would be to change the exp cost for training/studying.
Unfavoured guilds' guildmasters have more spare time to teach and teach at a
lower ratio (1 to 1 as opposed to 1 to 10 or something), and therefore you
learn faster. Busy guilds would be penalized since the GMs are busier and the
quality of teachings are worse (cost more exps for training/studying).

Sir the Master Merchant
For Pricing Information - "finger sir"