I have used Collect Plus which is when you drop the parcel off at your local collect plus shop (usually a newsagents). For a 10kg parcel it cost 3.49 for the recipient to collect from their local collect plus shop or 6.99 to have it delivered to their door.
Parcels Please is 5.19 + VAT for a 10kg parcel door to door.
Parcel Flight is 7.99 for a 25kg parcel door to door.
Have you tried any of these?
Have you used any cheaper ones?