Personally I find that when you go to buy your CND products and you hand the cash over you tend to think "Jeez these are expensive", but I find that in the long run they are not so expensive really. Their products are good quality and seem to last a lot longer than cheaper brands. I tried NSI earlier on this year and their l&p doesnt seem to last so long, whereas I'm using a litre bottle of CND monomer at the moment which I think I bought in May and I'm still only about 3/4 of the way into the bottle. I've tried cheaper products before but I find them to be a false economy to be honest. The other thing to consider is that if you buy cheap products and as a result you produce cheap nails, your clients may well move onto a tech who provides quality nails with their more expensive products, and your cheap purchases wont seem so good then!
Why not get in touch with various suppliers and ask them to send you sample sizes of their l&p systems and ask how much their products cost. Then you can try the products and weigh up the balance between the quality of nails and cost of products and come to a decision that way.