Lucknow

Its fee is around Rs. 55000 for a year. Refer to the link for more clarity: https://www.srmu.ac.in/PDF/FeeStructure/Fee_Structure_UnderGraduate_Courses_Session 2017-18.pdf

National Post Graduate College and Integral University are the best options for B.Sc in computer science.

Both are good. But SRM, Chennai has a plus point in terms of placement and infrastructure. And, it is also a reputed private college in India.

Yes, 450 marks are enough to get admission in IET, Lucknow.

I would suggest not to concentrate more on the cheaper colleges. I agree, these days, the cost of education is very high. You cannot get affordable and best colleges together. The cheaper colleges are not good in terms of faculty campus and placements. The expensive ones are much better.
You can go for DU and JMI colleges in Delhi. They have comparatively lesser fee structure as compared to the private one.

Ramswaroop College, Lucknow is a good college.

Hi Akanksha,
Please go through the link below:
https://www.shiksha.com/mba/colleges/mba-colleges-india?uaf[]=location&ts=2097540&rf=filters&ct[]=138&ed[]=et_20
However If the college is affiliated to AKTU (formerly knows as uptu) then I would suggest you to please save your time and money by not taking admission.
Hope this helps.