"This is the valid price."
Translation:Ini harga yang berlaku.
I feel like another alternative to this sentence would be "Harga ini berlaku".
I think there is a subtle difference. If I was bargaining over the price, the seller might say, Ini harga berlaku = This is the (valid) price ... meaning that this is the price I will offer. Ini harga yang berlaku would be what would be said if I queried the price ... e.g. Is this the price with the discount? I may be wrong, but 'yang' usually adds some specific meaning ... but not always.
This is the price we can do.
Berlaku indicates to me that something can be done.
To me indicates that is a price that can be done.
Surely validity would be like benar or betul etc