Weasel, you could do this:

on *:TEXT:*:#: {
  if ($1-2 == !buy halfop) { .mode # +h $nick }
  if ($1-2 == !buy op) { .mode # +o $nick }
  if ($1-2 == !buy voice) { .mode # +v $nick }
  if ($1 == !opstore) { .msg # $nick you can buy op halfop voice :-) just say !buy <item> }
}
on !*:JOIN:#: { .notice $nick New op store! !opstore }