There are no real shortcuts. In order for corals and anemones to thrive, they need great water conditions. Mushroom corals and some leathers are pretty hardy but, any degrading of water quality is gonna effect them, keep that in mind in whatever you choose. Anemones are even more sensitive and probably not a good choice if you are trying to be frugal with your set up. Not sure what lights you have (you may have mentioned it) but if your tank is in good shape with good water quality and lighting, try some mushrooms. See how you like them and go on from there. Just keep in mind that the corals won't be as tolerant of nitrate levels that your fish are. Another option that would help make your tank look more natural and would actually be beneficial would be to add some macro algaes. Also, if you have a mind to, add some sponges. Both will benefit the tank by reducing nitrates and sponges harbor beneficial bacteria which is helpful to the tank. I've included a link for you to check out on sponges. Also, I forgot to mention before, serpent/brittles stars would also add some interest to your tank. Good luck.