25% markup over the same sort of meal is reasonable.
The trouble is that tuna rolls at a Michelin-star restaurant in London are $18-$23 a portion, depending on which one you choose. Bear in mind that Michelin-star restaurants can charge a premium that Miami can't, because they're selling better-quality food and (usually) deliberately don't have quite enough seating to fill demand on a regular evening, let alone peak.
If one decides the Michelin-star restaurant isn't in a position to charge anything over the odds, and even if one assumes the Miami food was Michelin-star quality (obviously it wouldn't be able to acquire one ahead of the event and I don't think they carry quite as much weight in North America as Europe in any case), Miami would be right at the top end of that. However, the availability thing most Michelin-star restaurants have means this is unlikely to be the case. Both manufacture a captive audience in different ways.