Well, Thailand is not a cheap travel destination as it appears to be, but still, I would say that it is affordable for Indians. The cost of living is almost the same, but when we do conversion we multiply by 2 and it gets doubled. For instance, a domestic beer would cost you 80 THB but if you look at in INR it is 140. A bread cost you 30 THB, so it would be Rs.60. Now, we know how much bread costs in India:).
When I traveled solo to Thailand, my expenses were 42k which is reasonable. It totally depends on how you spend. For 7 days of budget travel, it would be 55–60k or more in case you plan to spend extravagantly. I would still recommend you to carry not less than 80 K if you are going with friends. If you are going with family you should have a minimum of 1.5 L at your disposal.
Few tips to save money:
Avoid Tuk-Tuk rides, they charge you outrageously or need to bargain more to get a reasonable deal.
Taxi is good and drivers are professional. If you are traveling more than one person than a taxi would be reasonable because metro fares are not very cheap- one side metro ride would be 30-50 THB minimum. But if you are traveling with family, both the options are good. The language would remain a barrier with taxi drivers and you may need to call their customer service for translation services- which free of cost.
In Bangkok, go for travel cards valid for 24 hrs or maybe 3–4 days.
For other destinations, Phuket, Koi Samui, Pattaya use ferries for transportation. They usually charge you 10–20 THB for one side fare. Ferries are spacious but speedy.
Carry your packed food ready-to-cook unless you really want to try Thai food. You may not find everything palatable but still, Thail street food is good in taste if you are a seafood lover.
You can carry Thai Baht with you as you may get pretty good conversion rates here rather than using cards in Thailand. Baht is common currency so it would have less brokerage charge.
For cards, you must check the conversion and service charges by your bank – which is a good option to use to travel to some countries.
Water ferries rides could be higher and they may pitch you 1600–1200 THB, near Chao Pyra river Bangkok. You can get as cheap as 800 THB for the river tour. You need to do find out find by yourself as there would be a lot of options.
For cheaper and a decent shopping go MBK center. You can get good deals on cameras, mobile, cosmetics, apparels, and electronics. This mall caters to the need of middle-class.
For more cheaper shopping try Chatuchak (street market), Indira, and Pratunam Market.
There are other malls like Siam center which is meant for sophisticated shopping.
Explore temples and palaces, Bangkok
Grand palace is for 1000 THB (Must visit)
Wat Pho (100 THB or maybe 200 THB max, They will give you free complimentary water bottles)
Wat Arun- Across Chao Phraya river, you can board ferries for 5 THB or sometimes free if the footfall of people is high.
Overall, Thailand is a good travel destination, colorful and vibrant other than what it is being known for :). It is cheaper due to the wide variety of options but depends on how you spend.
Make good use of convenient stores present in every corner. There are two supermarket giants, Seven-Eleven and Family mart. Both are amazing but seven-eleven is really good. Alcohol is easily available in stores but not after 12:00 am.
I hope this helps you to some extent.