The Cheapest Xformer set I know of rated at 100W runs about $150 retail. The cheapest Sovtek 6L6s or EL34s go for about $25 a pair. It takes 3 pair to get to 100W. Add in however many 12AX7s at $15 per. Include the cost of tolex, wood, speakers, the chassis, metal corners, jacks, pots...