How about not selling exp in any form (make it sacred, untouchable
) but putting on the talked about sub (via gg as LB says) but make it a condition to be able to log in and make it from higher level than euro level 7, like 22 or better, 33, or even 40? Levels under 40 are these days usually considered 'pre-game', like something to get over to get to the new stuff.
But I can see how sub condition to log in could kill a server, so how about giving perks instead but not exp buffs, say exclusive access to cave teleports (to some or all, at lev40 you would lose it unless subscribed).
I had an idea if subscribed accounts could have daylight in caves or gain access to more powerful lamps than normal? The mentioned exclusive mount skins would be nice too.
EXP is a huge incentive and getting alternatives that people would pay would be tough, awhile ago I was discussing the following for a subscription
(it did have an exp bonus but lets rule that out to see peoples feedback)
Elite Buff
(1000GG for a 1month buff, its not timed its based off a list so when your name is removed from the list, you lose the buff).
(Consecutive Months are 750GG)
GameGold Scrolls give you Twice the Reward Value.
You get 30% increased Kill Points Rewards when killing bosses
You have Exclusive Access to a "Night Dojo", that is a safe zone and gives you 2x exp for spells (only open at certain times)
You have Exclusive Access to a "Fishing Maps" these become accessible at random times, and again are safe zones.
You can use the EliteTigerMount (DC/SC/MC0-1) obtainable from the same NPC you buy the buff from.
Champion Buff
(1500GG for a 1month buff, its not timed its based off a list so when your name is removed from the list, you lose the buff).
(Consecutive Months are 1200GG)
You get 750 GG each month
GameGold Scrolls give you 2.5x the Reward Value.
You get 40% increased Kill Points Rewards when killing bosses
You have Exclusive Access to a "Secret Dojo", that is a safe zone and gives you 3x exp for spells (only open at certain times)
You have Exclusive Access to a "Fishing Maps" these become accessible at random times, and again are safe zones.
You can have a second go at the "Infinity Tower"
You can use the ChampionWolfMount (DC/SC/MC1-1) obtainable from the same NPC you buy the buff from.
Kill Points are an in game currency (same as GameGold - seperate shop for it) but only obtainable by killing bosses, doing achievements / some quests.
Infinity Tower is a challenge you can go in once a week, you proceed through harder floors, the person who is ranked the highest get rewards (there is a separate rankings page for who hits the highest floor / completes it) - 2nd/3rd etc can potentially get rewards also.