5in retic, if that what you refer to as a tea cup ray, go for $40-60 each by me. It can stay in that 150 for awhile. Maybe life time if it is a 150 wide. Some may disagree that the retic may need more room. Just my 2 cents. Just make sure you have plenty of filtration, I have no probs with 2 plecos in my tank with my rays. But again some may disagree.
Just make sure your tank is cycled with good filtration before you introduce the ray. Also retics are hard rays to get eating. Mine took a week to 2 weeks. Make sure you got all types of food to try. Bloodworms, blackworms, nightcrawlers are usually the best. Keep the tank warm and dark. And GOOD LUCK!!!!