The slab cost about $30 and would feed 3-4 people. According to Dad, who's apparently been eating breakfast there, you can also get a slice for $8. We also had a sour cherry yoghurt cake, which came with sour cherry sauce, and was incredibly tasty, very tart and sweet.
Spanakopita itself is a spot I wouldn't mind spending some time. It has a minimalist interior with high ceilings, almost like a converted warehouse space, which seems quite unique for a Greek cafe. I didn't get to try the coffee or other cakes, but the baklava and bougatsa in the cabinet looked excellent. (According to this review, they are excellent, so that's good to know.)