This question is way too vague to answer because it's way too subjective. Ultimately the only person who it matters to if it's a "good deal" is you because what may be a good deal to you may not be a good deal to someone else.

After all, $500 for a round trip between North America and the UK? For many, a good deal. For others, it may not be a "good deal" because no matter how good the deal, they won't do an international flight in economy. The route matters too. $500 may be a great deal between the UK and North America but would be a terrible deal between say Seattle, Washington and Los Angeles, California, a route I've paid just over $100 round-trip for before. Conversely, $500 may be a good deal in US domestic market with little competition otherwise. Time of year matters too. $500 may not have been a great deal for a random week trip between Seattle, Washington and Detroit, Michigan (a route I flew frequently to visit family) but $500 over Christmas would have been a "good deal" because fares around Christmas sometimes went for $600--$700+ even in Economy.

Other factors are the airline. What is included in that "good deal". A "good deal" on Spirit or Ryanair with little more included than a ticket from A to B but then having to pay for anything/everything else is different than a "good deal" on a full-service carrier that comes with some amenities on the flight.