const file = [
  {
    "seatNumber": "1A",
    "price": "£19.99",
    "available": true,
    "disabilityAccessible": true
  },
  {
    "seatNumber": "2A",
    "price": "£19.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "3A",
    "price": "£19.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "4A",
    "price": "£19.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "5A",
    "price": "£19.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "1B",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": true
  },
  {
    "seatNumber": "2B",
    "price": "£12.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "3B",
    "price": "£12.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "4B",
    "price": "£12.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "5B",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "1C",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": true
  },
  {
    "seatNumber": "2C",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "3C",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "4C",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "5C",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "1D",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": true
  },
  {
    "seatNumber": "2D",
    "price": "£12.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "3D",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "4D",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "5D",
    "price": "£12.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "1E",
    "price": "£8.99",
    "available": true,
    "disabilityAccessible": true
  },
  {
    "seatNumber": "2E",
    "price": "£8.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "3E",
    "price": "£8.99",
    "available": false,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "4E",
    "price": "£8.99",
    "available": true,
    "disabilityAccessible": false
  },
  {
    "seatNumber": "5E",
    "price": "£8.99",
    "available": false,
    "disabilityAccessible": false
  }
]

const seats = file.filter( seat => seat.price.replace(/[^0-9.-]+/g,"") == Math.min(...file.map(function ( seat ) { return Number(seat.price.replace(/[^0-9.-]+/g,"")) }) ) ).map(seat => seat.seatNumber);
        console.log(seats)

O(10) ~= 211
 O(100) ~= 20,102
 O(500) ~= 500,005

function bestSeats(seats) {
     var min = Infinity, minVal;
     const result = [];
     for (const seat of seats) {
         const price = Number(seat.price.slice(1));
         if (price < min) {
             min = price;
             minVal = seat.price;
         }
     }
     for (const seat of seats) {
         if (seat.price === minVal) { result.push(seat.seatNumber) }
     }
     return result;
 }

function bestSeats(seats) {
     const price2Num = seat => Number(seat.price.slice(1));
     const min = (min, seat) => price2Num(seat) < min ? price2Num(seat) : min;
     const minPrice = "$" + seats.reduce(min, Infinity);
     return seats.filter(seat => seat.price === minPrice).map(seat => seat.seatNumber);
 }