Starting with a Nikon!

The Beginner:
The “entry level” mostly features upgrades of D3100 and D5000. These are targeted at enthusiasts who are just entering the DSLR field but have a strict budget restraint. Take for instance the D3300 DSLR (priced around BDT 40,000 body only, with 18-55 VR II BDT 48,000). For example, the semi pro D7100 has 51 Autofocus points, 11 of them are cross types (can focus in extremely difficult situation), whereas D3300 has only 11 and none of them is cross type. Entry level cameras don't have any built-in auto focus motors; these cannot auto-focus older lenses that don't have an internal focusing motor. So you pay more for the auto feature. The legendary 50mm prime 1.8/D costs only BDT 8,500 whereas its Twin brother 50mm 1.8 G (with motor) costs about BDT 20,000.
If you plan to shoot in the dark a lot, don't get fooled by ISO numbers of 12800 of D3300 or D5300. These are hardly usable. The new D3300 has an amazing noise performance up to ISO 6400 which is quite remarkable at this price range. Semi-pro models like D7100, D300s can shoot at higher ISOs without getting affected by too much noise.
Speaking of image quality, Nikon has started a revolution by omitting the OLPF (Optical Low pass filter) from their image sensors in recent cameras like D5300 & D3300 (first introduced in D7100). This enables you to take super sharp images and to use your sensor's full capacity. OLPF was included in past cameras for avoiding the Moiré patterns by softening the image.
In my opinion D5300 is a bit of a waste of BDT 15,000 extra to get a rotating LCD (BDT 55,000 body only). I will suggest getting the amazing D3300 with 18-55 VR II (a super sharp lens at a very cheap price) if you opt to take occasional family or landscape pictures. No internal motor? Not a problem as all new Nikon lenses come with internal motors. And yes there is Full HD video. I wouldn't suggest D3200, D5200 or D5100 as these models are getting obsolete.

The intermediate pros:
For more serious users, I don't recommend a full-frame camera initially unless you want to start with sports or underwater photography. Full-frame has big advantage in noise reduction in low light shots. As their image sensors are larger, you can utilize higher ISO in the dark to get brighter images. How it works? A 24 MP FX sensor is 1.5 times larger than the cropped one. Therefore pixel size is bigger. So one pixel can capture more light data, thus producing such low noise and high details. But, in most general cases you won't need more than ISO 3200. Besides, FX bodies and lenses are way pricey. For example, D7100 has almost the same picture quality of D610 (FX) but costs BDT 55,000 more! Go buy good lenses instead. Fun thing is lens compatibility is higher for DX bodies. You can use FX lenses as well as cheap but excellent DX Nikkor lenses.
For the mid range user, D7100 is absolutely an outstanding performer. It is presently world's best DX/crop sensor camera (see DXOMark or snapsort rating of it). Weather sealed and strongly build coupled with expeed 3 sensor and ground breaking dynamic range, this camera will get most things right.
D7100 renders colors and white balance quite accurately. Seems Nikon will not release the anticipated D400 (successor of Legendary D300s) as D7100 suffices. Priced at BDT 75,000 taka (only body) and with excellent 18-105 VR lens it's about BDT 93,000. There is no point of buying D300s (very rare in market now) with BDT 120,000 (yes you read that right) which is highly overpriced and no match for D7100.
Then there's the D7000 with similar picture quality (but poorer processing, MP, white balance etc.) At BDT 56,000, you're actually better off ignoring this and going for the all-time legend D90 instead. It's selling at BDT 43,000 body only and provides beautiful color tones and noise performance and its build quality is rock solid. It's one of the biggest sellers and Nikon is still producing it. Video is rubbish though.

Conclusion:
Digital imaging has progressed tremendously over the last five years. Low range models always were chasing higher megapixels as users of this range are only concerned about the myth of high megapixel.  But the current batch of new entry models also focus greatly on image processing, dynamic range, color depth and white balancing.
So bottom line? As a newbie you can look into D3300 for starters. With more money and more professional requirements, opt for D7100.
 

Write is chief photographer/ founder of Adroit Productions and big fan of Nikons, obviously.