We went at October hand term - me (50s), dh (40s), ds(15) and dd(15). Ee eevtbti the Blue Lagoon 5 days before it closed!
We grew on Iceland Air and they sold bus tickets into Reykavik on the plane. The bus was waiting outside the airport and it was about 45 mins to Reykavik. (It was slightly convoluted in that the bus took us to a central depot, then directed us onto smaller buses that took people to their hotels). The dc were half price, and it was about £90 for all of us. We booked a taxi to go back to the airport a few days later (very early start) which was about £120.
We booked all our excursions via our travel agent before we went, but our details were lost/not passed on in a few cases, so I'd get busy on Google and book direct. There are only actually a few tour providers "on the ground" . Nice Tours seem to be popular!
We stayed centrally in Reykavik and walked everywhere we needed to go in the city,
The excursions we did - Golden Circje tour, Northern Lights evening cruise, whale watching cruise and the Blue Lagoon. We had a day of pottering too.
We didn't find earring out too bad at all:
Street Food Station - About £15/head for meal and drink. Really tasty fish stew - https://www.facebook.com/profile.php?id=100083399562338
Hippy little cafe on the Rainbow Street, good for cakes and hot chocolates! https://www.babalu.is/menu.html
Reykavik Fish - massive fish and chips, also burgers etc, about £23/head - several branches around Reykavik https://reykjavikfish.is/
Food hall, The Tacos from Fuego Fuego were awesone https://www.hlemmurmatholl.is/english. Was £25/head ish for meal and drink
Lebowski Bar was right next to where we were staying. We didn’t eat there, but it looked fun and reasonably and they do a Happy Hour 4-7 pm https://lebowskibar.is/en/
Braginn - chips, Tacos, burgers etc - in car park for geothermal beach at Nautholic Beach where I went for a swim. About 30 mins walk out of time.
The biggest price shock was £55 for 4 Subway meal deals!
We were self catering, and shopped at "Bonus" - a budget supermarket similar to Lidl etc which was maybe 20% more expensive than the UK.
By the time we left in early Nov, daylight was about 9am/4pm and average temp was about 0degrees C. The travel advice we got was that, if we had to stick to school holidays, then the best balance of dark/light/seeing nothern lights/cold, was the go at October or Easter. I'd Google sunrise/sunset times and temperature before commiting to Feb half term. Even in November, we only just made it round the sights of the Golden Circle in daylight. We definitely wouldn't have seen the whales we did in darkness either. There a reason why February is cheaper than Easter.
But, as a geologist married to a geologist, we had a great time, and even the grumpy teens were reasonably impressed.
Everyone spoke English too. The tourism and hospitality industries are very international - the only Icelander we met was the pilot of the whale watching boat.