From looking at your profile gear, here are some options you can use for your level.
Get rid of the shield earring with -10mp and get either onyx earrings (2k each) for 2mp each or just go without earrings till morion earrings (9k each) at lv30.
Mohbwa Sash at Lv20 mp+10 (5-10k)
At Lv26, Holy Phial would be since it has mp+ and mnd+ which is good for whm. (5k)
You could also get rid of your tunic and buy a Cobra Tunic with 8mp (6k) or wait till Lv30 for Seer's gear, but would suggest getting a Silver hairpin with mp+15 (2k)
As for rings, you could probably hold out till you can get a cheaper alternative.
Something that would help with downtime in an exp pt is try to get some hmp+ gear like Pilgrim Tunic +1hmp (1k), Pilgrim Wand +2hmp(Nunyenunc NM), Mohwbwa Sash +1hmp (5-10k), and use Cinna-Cookies +4hmp (4k for 99). This will let you recover 8 more mp per tic, which adds up quickly.
These are just cheap and easy ways you can boost your mp.