Walmart offers the Franklin Soft Tip Dartboard, model no. 3560, for $19.99. (Amazon charges the same with free shipping for Prime members.) Choose in-store pickup to dodge the $4.97 shipping fee. That's the lowest total price we could find by $3, outside the mention below. This 18" x 1" dartboard includes six soft dart tips and six replacement tips.
A close price: Target has it for $21.37 with free shipping after coupon code "BESTGIFT".