When I first started I had tons of people try to negotiate price and many who would express shock over my prices which were much lower then. Eventually the people who appreciate this kind of work and who can afford it will find you (or you find them) and you will have less of this.
I rarely hear this anymore. One thing that helps is for you to be very solid and confident in your price. If someone does ask nicely why the heck so much for a cake, I simply explain that it's not the cost of flour and eggs but time spent on the artwork. Don't be afraid to say yes that's the price and wait for them to fill the silence.
I do bend over backwards to give them lower priced options, but I don't back down or feel guilty for any prices I set.
Btw, your price sounds a little low to me.