Let me quote an example for costs of packet seed versus loose.
There are between 3,000 and 6,000 peas in a kilo. Let's take the middle ground and call it 4,500.
That famous store beginning with "W" sells 300 Kelvedon Wonder seed for 97p. That would be 15 packets and cost a bit short of £15 for a kilo.
My local nursery sells a kilo loose for 1/3 of that cost.
Even ordering a kilo via post from Moles seeds would only cost £8.30.
I know most people would not want a kilo, (but remember stored properly these would last a few years or you could share), it's quoted by way of showing that it's worth trying to find a local, usually independant, nursery or allotment association, failing that ordering from somewhere like Moles.