VB:Search/Replace of text in large files

I have a very large text file (1 MB) that I need to search and replace pricing data. It can’t be a general Search-and-Replace function, since these prices are for the specific item it is for. There is one line of product data per line, but each line is very large, so replacing the entire line would not be feasible.. also, I need to replace two prices per line. I was thinking that the easiest way is to search initially for the item name I need to change, nab that whole line, replace the values, and then input them back into the file.. but is there a better way? (Or if not, how would I go about doing the above theory?)