Surface area of one bigger box =`2(25xx20xx20xx5+5xx25)`

1450 `cm^(2)`

By adding 5% overlaps =1450+72.5=1522.5 `cm^(2)`

Area for 250 bigger boxes =1522.5`xx`250 `cm^(2)`

cost for 250 bigger boxes =`1522.5xx250xx(4)/(1000)`=Rs 1522.5

Surface area of one smaller box =`2(15xx12+12xx5+xx15)=630 cm^(2)`

By adding 5% for overlaps =630+31.5=661.5 `cm^(2)`

Area for 250 small boxes =`661.5xx250xx(4)/(1000)=Rs 661.5`

Total cost =1522.5+661.5=Rs 2184