1. How much would I need to give an area approx. 60-70 sq m a decent
layer for seeding?

2. What should I be prepared to pay?

You get what you pay for.

Damn! I thought this was going to be a discussion about podsols, gleys, rendzinas and the gouy layer/cation exchange

I'm so disappointed :(

I honestly don't know, this sounds like a job for Gardeners Question time or the great Monty Don.

1. How much would I need to give an area approx. 60-70 sq m a decent
layer for seeding?

2. What should I be prepared to pay?

What's there now? Bedrock?

Depends on what you want to grow. The requirements for grass or potatoes differ somewhat.

Mainly lawn to start with then I'll move onto more complicated stuff (my dad and my sister have the monopoly on green fingers in my family!).

It's OK now - I saw the gardener at work at lunchtime and picked his brains for about 20 minutes so I have a very good idea of what I need to get and do...!

thought this was going to be about a gardening program spinoff from topgear ;)

Search the BBC database. I once saw a very inspiring docu on how to use waste water and such.

Tea/coffee > rhodondendrons a.o.
cowdung > roses
phosphates (bathwater) > loads of flowerplants think it's yummy!
for a lawn, just ask your local club's groundsman! But in the UK the soil is already well suited for a lawn, hence your excellent dairy products.

I scatter garlic peels around the garden which helps against spiders, fungus etc.

spiders are good bugs tho!! you're persecuting the innocent! cruel monster! ;P

I'm only keeping spiders away from some plants, a web plus moisture makes a breeding ground for fungus.