Unsure about pricing (there are websites out there that can give ballpark figures) but about needing an electrician, that would depend on how handy you are. You're allowed to replace existing fittings without authorities demending to put their nose into your business. Lighting electrics aren't difficult but one needs a basic understanding, care, and common sense. If I could lift the chandelier easily and wanted the job done, I'd DIY it. Just ensure one screws into the rafter with sufficiently large screws, (no screwing through cables) and connects the new fitting identically to the old. But others may want an electrician to have the responsibility.