There will be a local builders merchant close to you no doubt and the prices will be 25% lower and more than the big superstores. This is my own recent experience.
There is a local shop near me and I went in and explained I was building a Granny flat, proposed to spend around 10,000 lv with a supplier and asked for a further discount.
I negotiated all materials shop prices -8% and -5% on cement as the margins are low for this apparently. Worked out well for me to the tune of around 700 lv.
I shopped around a bit though and as per a previous post this is the way to make savings.
My concrete path slabs I bought from the same company that supplies the town footpaths so had to go into the town hall and get his number etc etc. Double the price in Baumaxx so was happy to do this. 10 minute conversation saved me 500 lv.
It is hard to say what the general prices are, they are definitely cheaper than the uk but I would not know the costs in the UK to the penny...
My advice is to buy where your neighbours buy and ask them a lot of questions, people are very nosey so interested to help you as they get info on what you are doing along the way and can discuss it on the benches in the street
List out 5 materials you want to know the price of and i will digout my receipts.
That should give you a ball park.