Walmart has ONN Digital Signal Amplifier for Indoor Antennas on clearance for $3 in store only, as with all Walmart B&M clearance this is YMMV. MSRP $14.96.
Walmart product page: https://www.walmart.com/ip/ONN-Di.../139204884
In my local store they were on a rack near an aisle end in electronics and the price on the rack was $7 but it rang up at $3.
Check Brickseek for approximate inventory & pricing here: http://brickseek.com/walmart-inve...=139204884
Nearly every store in my area  has them in stock and at $3. YMMV.
Pretty cheap if you have an OTA setup and some channels are iffy. This will not help you get channels that don't come in at all, only potentially improve the signal of those you do already receive.