robot navigation system

Hi there

I am building a beverage delivery robot to bring me drinks for in door use. everything is going quite well, but there is a problem, I have no idea how i should do the navigation system. I looked at quite a lot sytems. i first wanted to make it move by a known map but i read that it wasn't very precise and very expensive. So i think i want to make it move by a default route and it will go off that route if something is in front of the robot and when it passed the object it will go back to it's route, and at it base station there would be something like a IR beacon to re-sync to it's route. I don't now how i should start, so if somebody could help me i would be really grateful.

what hardware i have: - dagu rover 5 with 2 encoders - 2 ultrasonic distance sensors - IR receiver - 2 LDR

Get a UV-visible marker pen and draw a line on the floor for your preferred route.
Swap the IR LEDs on a line-follower for UV LEDs.
Make sure your visible light receivers are filtered to remove UV.