let's see if I get u right：你是觉得 to pay for 是主动语态,to be paid 是被动；而人是主动的,钱是被动的,所以似乎应该说 fifty pence is a small price to be paid.
但实际上,sth to do 一般本身就含有被动的意思了.
例子,我们常说：Do you have something to say?/Do you have something to do tonight?
而不说：Do you have something to be said?/Do you have something to be done?
这是因为这些句子中,谁是主语谁是宾语太明显了,不需再用 to be done 强调.
我觉得哈,为了便于理解,你可以把那句话看成 fifty pence is a small price (for sb.) to pay for.
十分看好你细致入微的学习态度哦~~~加油!