A press release from LonCon 3:

Loncon 3 is pleased to announce a special May holiday sale on Adult Attending and Young Adult Attending memberships. Adult Attending rates will be reduced to GBP95 (US$160), a discount of GBP10, for all adults joining online through the Loncon 3 website between Friday 24 May and Monday 27 May (which is Spring Bank Holiday in the United Kingdom, and Memorial Day in the United States,). An equivalent reduction will also apply to adults upgrading from Supporting to Attending status. The Family Attending rate will be reduced to GBP230 (US$390), a discount of GBP15.

The reduced rates also apply to all face-to-face membership sales made at BayCon, ConQuesT and WisCon between Friday 24 May and Monday 27 May.
The sale does not apply to mailed-in memberships, nor does it cover the installment plan.

Loncon 3 co-chair Alice Lawson said, “We are delighted to be able to offer this special opportunity for new members to join — or for supporters to upgrade — so that as many fans as possible can come to London next year.”

Co-chair Steve Cooper added, “Loncon 3 is already on course to be one of the biggest ever Worldcons outside North America, with over 3,000 members
already signed up — 2,500 of them as attending members. It will be an occasion not to be missed.”