wow thats a difficult question, iv pretty much now replaced every nut and bolt from under the car but iv bought in bulk due to the discounts i get at my local fasteners. I also had to special order a couple of bolts as ford done a couple of sizes that my fasteners had trouble getting hold of. I would say you could do the underneath for sub £50. Its so difficult to remember

P.s Just thought i would mention that most ht bolts are designed to be used only once so most of the bolts should realy be replaced once removed