From the Southwest website:
*Points will remain active as long as you have at least one qualifying earning activity every 24 months. Qualifying earning activity includes 1) completed revenue travel on flights flown through Southwest Airlines® and posted to the Member’s account prior to the expiration date; 2) points earned by transacting with any current Southwest Airlines Rapid Rewards® partner (including transfers from applicable Rapid Rewards partners and completed Southwest Vacations® hotel stays) and posted to the Member’s account prior to the expiration date; 3) points earned using Rapid Rewards® Credit Cards and through points transferred from Diners Club® and posted to the Member’s account prior to the expiration date and 4) points purchased for personal account use through Southwest.com and posted to the Member’s account prior to the expiration date.
Pursuant to number 4, it would seem that you can purchase 2,000 points for $60 and keep your points active (provided that they post before the expiration date).