Walmart offers the Antec Bias HDTV Lighting Kit for $16.65. Opt for in-store pickup to dodge the $4.97 shipping fee. That's the lowest total price we could find by $3. This kit includes six red and blue LEDs.
Update: Fry's offers it for $9.99 with free in-store pickup. Alternatively, Amazon offers it shipped for $11.98 with free shipping for Prime members.