1. Since you’re headed for the islands in the south, I’d suggest Diwali time. You should get there just after the end of the rainy season, and the weather will be pleasant. Remember too, that this is a grieving nation: the recent death of their beloved king has resulted in a year-long period of mourning, when some attractions will remain closed. November 2017 will mark the end of that period.
2. Bangkok offers a wealth of accommodation. Several small hotels offer stylish boutique stays for a little over your budget but if that’s not your thing, stick to ibis Hotels. They have a selection of no-frills hotels conveniently located around the city, and cost approx. ?2,500 a night (ibis.com). It’s very, very hard to go wrong with street food in Bangkok, and part of the adventure is trying out stuff for yourself. However, the most popular areas for street eats are Chinatown, Bang Rak and the Old City. The trick is to snack and move on, so you can try a decent sampling from the staggering range. If you’re fastidious about hygiene, just head to the nearest mall, descend to the basement where the food courts are usually located and do the same: sample wares at the plethora of stalls you will encounter. No, they’re not expensive. And I do hope you’re all non-vegetarian.
3. If you’re looking for quiet beaches, I suggest you drop Phuket forthwith. Head to Krabi instead which, while touristed, still has unspoilt stretches. The cheapest and most convenient way to get to Krabi from Bangkok is to take a bus from Bangkok’s Southern Bus Terminal (12hrs). Krabi hotels in your budget: Apasari Krabi (apasari.com), AliSea Boutique Hotel (alisea boutiquehotel.com) and Poonsiri Resort (poonsiriresort.com).
4. Krabi also makes sense because it’s a connecting point to Koh Lanta—1-2hours (70km) south, by ferry or mini bus. In Koh Lanta, Klong Dao beach and Long Beach offer the most variety in terms of accommodation and tourist services. Attractive and affordable options are Lazy Days Bungalows (from ?3,000; lantalazydays.com), Relax Bay Resort (from ?2,000; relaxbay.com), Chaw Ka Cher Tropicana Lanta Resort (from ?3,500; chawkacherresort.com) and Long Beach Chalet (from ?1,800; longbeachchalet.net).