I don't know the cost of cards (and can't check from work) but if you plan on having no other creatures besides chrysaora, then sundial is a natural fit, and I'd do my darnedest to get some of those in here, probably by dropping holy lights and/or the graboid/heal, depending on preferences.
One card I think would be very good here is to try and get a nightmare or two in here. Nightmare a chrysaora, for example, and unless your opponent has death and water, they can't even use them. (and if they do, just don't nightmare it :p) Nightmare can often provide about as much healing as holy light, as well as deal equal damage and clog their hand, although it is countered by sanctuary. Though, if your opponent is playing a lot of healing permanents like that, you're in a lot of trouble with a deck like this, anyway.
If you don't like sundial and/or nightmare (or they can't be bought with a starter) then lycanthrope would be a good fit, using two elements that aren't in use in this deck, for a strong, cheap attacker, but I would not use more than one or two with this quanta base.