Dive in and do it yourself. I did my first one working from the readers digest manual.
Its not difficult, honest it just requires the confidence to do it. Find the main water off valves for hot and cold, use speedfit end caps when you rip it out and then do your connections using speedfit when you fit the new one. Take your time, buy 20 quids worth of bits of plumbing pipe and fittings to practice on and you'll crack it.
I found B&Q's book You Can Do It. the complete B&Q step-by-step book of home improvement (ISBN 9780953524341) invaluable, ok its £20 in store but well worth the money and covers everything thats needed to make repairs and tells you how to do it in stages. I've just bought my first home last March and have fitted new lights drainned the radiators built a concrete shed base and steps, patio, Log Cabin, landscaped the large garden, put in a large pond, changed all the lights, tiled the kitchen floor and walls,Skimmed and plastered walls, new skirting boards, Kitchen units, plumbed in the kitchen and bathroom, fitted new taps and drains to bathroom and electric bedet. I couldnt have done it and wouldnt attempted it without the book. get yourself a coply it will save you £££££.