sis keziah1219, just got back from BKK last sunday. We stayed at Vista Residence Bangkok.
http://vistaresidence.com/en/default.htmPros:
- cheap
- clean
- Bfast included
- fast wifi
- big rooms, with safe box
- near BTS national stadium station,
- walking distance sa MBK Mall, Siam Paragon, Siam Discovery
- 10 mins to Platinum or Pratinum Mall via taxi (THB 50)
- friendly & accomodating staff
- taxi from airport to Vista residence (THB 350 including tollfee and surcharge)
- taxi from Vista to airport (THB 250)
- they have a small resto. cheap, clean & masarap yung food. maraming students & locals na kumakain dun. (meals costs around THB40-60)
Cons:
no elevator kasi 4 floors lang but they will assist you naman with your luggage.
or you can try Lub D
www.lubd.com/We were planning to stay here, kaso fully booked sila. So i cannot give a review. But it looks cool and malapit rin sa MBK mall.
TIP: bring USD instead of Peso. Mas malaki yung exchange rate ng USD. Last week it was around 31.57 sa MBK mall ground floor. Sa airport it was just 30.28 . Peso was 0.52 lang sobrang baba 
For your budget, it depends on your itinerary and shopping power hehe. I can give you the entrance fee na lang and estimated fare.
Tourist Spots:
Grand Palace = THB 400
(from BTS National Stadium station to Saphan Taksin Station= THB 30 / Tourist Ferry to Grand Palace THB40 / pag yung regular ferry lang THB 15 kaso nakakatakot sobrang puno yun )
WatPho = THB 100
WatArun = THB 50
(Round trip ferry from WatPho to WatArun= THB 6.00 )
(Ferry Back to Central Ferry Station TBH=15)
(BTS back to National Stadium = THB 30)
Ayutthaya = we took a package tour na lang para less hassle. THB 1,200 wholeday Ayutthaya & Banpu Palace tour including lunch and hotel pick-up.