If you're lazy the best way is to invest in guthans for nmz, for steady afk combat exp, otherwise slayer is budget, to earn some cash / level. not many other ways unfortunately other than just training monsters like yaks / rock/sand crabs
What are your stats if you don't mind me asking, I've been planning on doing barrows recently just not sure if I'm ready.
Also, do you have the diaries done for extra l00t / is it worth doing without the diary? sorry for all the questions xD