hi Smiley.
difficult question to answer straight off as there are so many variables involved, I will put a quick list down to give you some idea what I am talking about, but essentialy it is possible to DIY as I have done it several times in the past,
1. first is obvious, have you checked that the old bar will fit new car, subtle differences in models can make a difference for instance the bar for a mk3 may well not fit a mk4, the bar for a saloon may well be different to a hatch or estate.
2. have you enough DIY experience and the correct tools to do the job, (also a workshop manual would be a good idea) as this highlights the order things are removed and replaced plus hidden fastners torque figures ect,
3, are you intending to transfer the whole lot like for like ie electrics same plugs wiring and so on, in this case everything on the old car must be removed relays, feed wires, ect, with a notes attached to the wires where they came from colour codes ect,
4. be aware that modifications may also be required, panels cut (behind the bumper foam) modified or removed and it is allways a good idea to replace old bolts ,nuts ect with new ones,
5. make a mental note of the job in hand before starting (how things are routed like wires?, what goes where? which way round bolts are inserted? things like that.
removing the old one is pretty straight forwards, replacing it is a little more complex but is possible,
ps, I have no idea of the going rate for a new bar if £375 is for fitting the old one thats exessive if its the cost of a new one fully fitted is not too bad, try priceing one for diy fit and see what the labour charge is,