Do we have the right to sue the govt or fil PIL against them

You can file a PIL. against Government. But pricing is a policy decision of the Government and normally courts would not interfere into policy decisions. 

but is it not wrong to decide pricing like this? what can we then do against it?

Yes, section 79 CPC is clear about it, but as pointed out by Y.Prakash Ji, the matter is covered by the Cynamide India Ltd. 

Do any Govt. has right to do pure bussiness at the cost of public money? It is a competition era, do govt. has right to remain in bussiness?

As a citizen of India and in the interest of public you can file a PIL against DTC.  Citizens have power to change policy matters if necessary. We are tax payers, we have every right to question the Government regarding increase of fares. Common people suffer a lot. Why don 't Govt. put heavy taxes on luxary items? Why did Govt. squeez money from common people?

Thanks sir, Generally govt. used to have more overhead expenses compared with private one. Govt. is not here to do any kind of bussiness for their profit at the cost of the general people. If it is for the welfare of the people then it is ok.

i feel you may raise an RTI query with the concerned authority asking queries like:

1} was there any committe constituted for raising busfare?

2)copy of the minutes of the meeting

3)what are the criterion adopted for reaching the increase

4)rationale behind increase of busfare only for "Blue line" as per section 4(1)(d) of rti act 2005.

these are some of the questions came to my mind immediately on reading your concern.well you can ask as many question like above.

make a campaign among your friends and relatives,let everyone ask similar rti with same authority.

i had suggested rti because of its economy and speed.

 general day 2 day routine work cant be advised to be done on the direction of the court is it proper? why we hav selected this govt havin corrupt minister lik powar ras--l ? who everybody is knowing has taken money from trader as himself is owner of 48 sugar mills alone???????????? ny clue ask the RTI PMO?????????

yes we can do something . because day-by-day the price of all the things is raising high and the poor people and the middle class people ant able to afford it .

so we can do ....

Unfortunately the judges are also govt servants and they have their own family to look after post retirement. Any PIL against the govt is there fore looked down upon by those learned judges . I am preparing to submit a PIL against the govt deptt for allowing running of URC ( unit run canteens ) by the CDA Staff/ Est to sale CSD goods to their employees who are not even eligible for the CSD facilities.