Postage from the UK is ridiculously expensive. A while ago I sold some boxed Amiga apps to a guy in Aus, and I was getting quotes of about £80 for shipping. IIRC the package was about 3kg, so your quote of £120 was probably about right. In the end I split the package up in to three different packages, the combined cost of which amounted to less than the cost of the single large package.
Was the package you got sent from Ireland from Northern Ireland? If not, it won't have been from the UK so probably wouldn't be comparable to UK shipping prices.
Edit - re. couriers, unfortunately I couldn't find any which were any cheaper than Royal Mail :-(
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moto