Thanks - that helps! I’ve been to a couple of the places you mention so :
Sri Lanka - we went last April (returning days before the bombing). We had 2 weeks there and had indirect flights on Kuwaiti Air - not ideal as we had 4/6 hour layovers but it was literally half the price. We really liked it - beautiful country and very welcoming people. We stayed in Colombo/Kandy/Tangalle and I used a local firm (happy to pass on their details, they were great) for transport. From Kandy we did trips to Dambulla/Sigiriya/Minneriya National Park/the Tea Country. Our transport costs were about £250. In retrospect I wish we’d taken the Colombo - Kandy train and stayed overnight at Sigiriya (it’s just too hot to climb mid day!). Pluses for Sri Lanka are beautiful countryside (the towns are less picturesque), plentiful wildlife (my DD really enjoyed
the jeep safari), fabulous empty beaches, good food, lots of history and lovely people. On the downside, where we were in Tangalle you couldn’t swim in the sea (but I’m not a big sea swimmer and you could see turtles bobbing about!). I’m not sure about the weather then either so just copied this over for you;
“Rainfall remains high on Sri Lanka's southern & western coast during October, with temperatures below their annual peak but by no means chilly! (avg temp: 28 °C). As per previous months, swimming in the sea is not recommended.
Things are also changing in Sri Lanka's north and along the east coast, with the arrival of the north-eastern monsoon. Rainfall starts to increase and the blue skies of the past few months will start to turn to grey.
Rainfall is also high in the Tea Country, although hot, dry weather is expected further north in the Cultural Triangle “
Goa I went to about 20 years ago and it might have changed quite a bit since! From memory there were more obvious signs of poverty than in Sri Lanka. The beaches were lovely - they did have cows wandering up and down them and people defecating though! There are some great markets and lots of tourists travelling around on mopeds - there was still a bit of a hippy trail vibe. The food was really great. Altogether it had a bit of a beautiful but rough and ready vibe (e.g having to carry loo roll round with you).
Costa Rica is wonderful - we went in August which is Monsoon season so if that’s what’s putting you off in October then quite honestly, it’s no biggie. We had a thunderstorm once a day for about an hour in the afternoon or evening. If your DC. like outdoor activities then it’s a great choice with zip lining/horse riding/rafting etc as well as a huge abundance of wildlife. If you re consider it and want info, there will be quite a few people on here that could help you!
I haven’t checked weather but if your DC liked the States then perhaps Miami then moving onto the Keys might be worth considering for a week and a half? Two weeks might be too much there.