could anyone tell me the value of solid sodium hydroxide per kg (or any other measurement if it's easier)?

Again - this will depend on the quantities you are trying to buy/sell. Might be worth looking in a chemical catalogue or at an on-line chem supplier for ball park figures. When you have descide what and how much you want to buy then ring (or e-mail) a couple of them to get some quotes.

If you are interested in buying lab-quantities, then have a look at one of the chemical suppliers. Sigma Aldrich is one.

 

If you are looking for bulk prices (if you're interested in 100 ton or more), then look at the magazines: for example Chemweek, ICIS. You'll have to subscribe to get this info.

 

Sadly, bulk prices of chemicals are negotiable when you buy them, and for that reason companies don't put prices on their own websites. The average bulk price is calculated by previously mentioned magazines... but they demand some money because they have to do a bit of research to get the number (and they list thousands, so in all that is a lot of work).