I hated knobby tires on my old MTBs because of the noise and vibration. I don't ride off road these days so prefer using tires with less aggressive tread. I used to buy tires from Niagara Cycle but they are out of business. The Kenda K838 were only $15 not including shipping but you can get them on eBay for $19 with free shipping these days
https://www.ebay.com/itm/1-one-Kenda...vNSL:rk:9:pf:0 or $35 a pair
https://www.ebay.com/itm/Kenda-K838-...gAAOSwFSRbj9ns If your tires show any sign of cracking or sidewall crazing it is worth the price to replace them. I just got in a Giant Yukon bike to refurbish for one of my Scouts and noticed the tires were cracking. This is the tire I will recommend to replace the knobbies on it now.