Amazon offers Prime members the Cricket Wireless BYOD SIM Activation Kit for GSM Phones for $2.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.01.) That's $2 under our March mention, the lowest total price we've seen, and the best deal now by $9. It includes a SIM card, micro adapter, and standard adapter.
Update: Note that this now has an estimated shipping time of two to four weeks.