Bestekmall offers its Bestek Wireless Doorbell Kit for $17.48. Coupon code "FORPRO60" drops it to $6.99. (You must be signed in to use the coupon.) With free shipping, that's the lowest price we could find by $2. It features a 500-foot operating range.
You don't need to hire a contractor or do extensive renovations to add value to your home.