Hi!
Check out Melo tours and Daytripper both have websites with itineries, we did the trip two years ago and it was fantastic, also saw a lot of the real India along the way.

We did a similar trip with Melotours in 2001. Can't recommend it enough.
We did a weeks trip round the Golden Triangle and Ranthambore Tiger Sanctuary, but if you can only spare a few days and decide to go in a car from Delhi there's a few things to see on the way, including the magnificent Lotus Temple and Akbar's tomb

http://www.bahaindia.org/temple/index.html

Fatehpur Sikri, another world heritage site is only 20 miles away from Agra.
http://www.visions-net.com/fs.htm

Have you emailed Melotours and asked for a quote and suggestions? They recommended us a car because we were going out of the way a bit.
The flights can be got for an awful lot less than 11000rps per person.
Not sure what they're charging for trips these days, but in 2001, a weeks trip from Delhi including the car, driver and 4* hotels cost us about £200..amazing value because Delhi can be stupidly expensive.

don't go air sahara or jet or indian etc. if you are a budget traveller. you have many cheap flights now like spicejet, indigo, goair etc. one way ticket from goa delhi is rs 4000 - 4500. book them through the net on yatra.com, makemytrip.com, ghumo.com. you will find them relatively cheaper.
hotels in delhi are very expensive, so book well in advance. you can get private coaches (don't go for air conditioned as it will be relatively cold in january) to take you to agra for about 500 - 1000 rs.
have a nice trip.

Ive never actually been, but we saw a couple earlier this year who live in Spain, and travel all over the far east. This was theie first time to Goa, and they visited the Taj. They said their experience was a nightmare. Lots of beggers as you reached the gate. Id understand a comment like that from someone who has only visited mainland spain or somewhere close to home, but these people are really well travelled, have spent months and months in third world countries so are used to poverty and begging.
They said they wouldnt be in a rush to visit the Taj again

Please do not let the last posting put anyone off visitng the Taj Mahal. Of course you will encounter some begging particularly in Dehli but this is the case in all India. We had no big problems at the Taj,but were bombarded with the usual souvenier sellers and people offering their services as guides or photografers. we didnt need them as Melo Tours provided us with a Guide who took great pride in taking a superb photo of us sat outside the Taj,even better than the Princess Diana one!Its well worth going a trip you will never forget.
ps I have also travelled world wide and the Taj gets a 10

Im not trying to put people off visiting, but this is what some people experienced.
Everyones allowed to have different views.