First of all there are entry-level tablets that cost around that much, based on Android or Windows, for example the . You can check if HDMI output is supported and plug in a keyboard and mouse via USB. You could also consider a cheap laptop such as the Asus X200 series.
If you want to assemble a desktop PC, here are some options. All prices approximate.
1) ITX motherboard with integrated CPU, for example the Gigabyte GA-J1800N-D2H (Rs. 4,200) (has USB 3.0 and HDMI)
2) Micro-ATX Intel H61 motherboard, for example MSI H61M-P20 (Rs. 2,700) (No HDMI/USB 3.0) + Pentium G2030 (Rs. 3,400)
3) Substitute Gigabyte GA-H61M-HD2 (HDMI, no USB 3.0) for Rs. 3,400
RAM: 2GB, any brand, Rs. 1,400
HDD: 250GB, any brand, Rs. 1,600
Case: As per personal choice, any brand, Rs. 1,200 - 2,000
PSU: Minimum 350W, should come with case, else any brand, Rs. 750 - 1,500 (get the best you can fit in).
KB/mouse: Logitech set, Rs. 800
OS not included in budget