Box it as small as possible – or not at all if possible – well bubble wrapped would probably suffice. Affix wood-batten between the rear dropouts for rigidity. Make sure the Trade Tarrif code (or whatever it is called) is on proforma’s and correct.
Make sure the marked value is nominal or as low as it can be (this affects insurance value [and therefore cost], tax liability and import duties). I am not advising using incorrect monetary values – because it may get damaged or lost, and fraud is illegal.
Specialist carriers I hate to say it – they offer unbeatable quality services but are expensive because they own fleets of planes, huge robot warehouses etc. etc.
I expect USPS would probably be the most cost effective – but not so protective. Try their calculator.
Last resorts – maybe take the family to Disneyworld on holiday, and bring it back in the hand luggage, or wham an advert on Craigslist to get some tourist to bring it in for you – a bit whacky – just depends on how badly you are strapped. Enjoy! 🙄
P.S. If I win – please dontate £2 to build a new Community Center in Glyncoch.