If you are planning to need a lot of live sand, maybe you could get a 50# bag of southdown and then seed it with other people's sand. That would probably be the cheapest way to do it. LS usually sells at $2/lb for a prepackaged deal, which is less viable than directly from a tank, which often goes for $4.99 a lb.
LR can be anywhere from $5 to $10 per lb, depending on the grade, origin of the rock, and other things. The cheapest way to get LR is to find someone breaking down their tank for some reason and buy their LR. I've seen $1/lb or sometimes even for free! But, it's relatively rare, and the demand is so high, you have to be REALLY lucky to get a deal like that. If you're willing to be patient, it will come. If you need it right away, then buying it from a reputable store or by mail order is easier. IF you go to a LFS, make sure they know what the heck they're doing. One of the LFS's nearby my place said that they dumped tap water into the tank, then dumped a bunch of salt. Their SG was around 1.021, and the employee said that they had fish die all the time. Duh! Definitely a Buyer Beware kind of place.
I'm looking to get some LR myself for my new 125 G. If I find an awesome deal, I'll let you know.