Please excuse me for perhaps being a bit "thick" but I'm still unsure as to whether the £115 is for the spring alone or is it the price for the whole job?
Am I right that "Livi auto parts" is Livingstone Auto Parts? If so, that's a supplier who's been around a long time and generally well known for competitively priced parts. They are going to be pricing this around that £30 mark unless something has changed greatly recently. They're a bit far out for me to use but always one I have kept in mind just in case one of the Edinburgh based suppliers - SRS, Pentland Components, Dingbro, ECP, Teviot Factors and others - who are more easily accessible for me, can't supply. Dingbro have always been strictly trade only but they allowed me to buy on production of my IMI membership card. However when I retired and cancelled my subscription to the IMI, like TPS, they wouldn't sell to me any more. I would expect Dingbro to be even more competitively priced than Livi Auto Parts.
As a final thought it's worth considering that the discounted price most of us will be able to benefit from by buying from a trade supplier, ie. a Motor factor, is usually not quite as good as the price which a volume buyer, like a local garage, will be able to benefit from. On a purchase like this I would expect the garage will probably get another couple of quid off.
I hope that the £115 is for the whole job because if it's just for the spring alone it had better be a solid gold one!