Well, there are always other ways to earn mesos than MP, but the nitty gritty of it is, is that MP is probably one of the best ways to earn especially considering the limited range and mobbing the Bishop class has to offer.
Here's a really mesos good guide by an AriesMS youtuber I watch for advisement, KEBIN (even though he only has two videos):
Some ideas he suggests are:
- Meso farming, coin farming
- Dailies such as bossing and sweetwater
- Monster collection for reward point farming (sell violet cubes)
- Selling services (such as HS for your class, Bishop)
All in all, there are other ways if you look for it, I hope you don't get discouraged.