A good way to save money when buying things online is to open a free account with Ebates. With Ebates, search for the website you want to buy from and Ebates does the rest.  Remember, it is always good to save any amount of money, no matter how small.  For example, if you are buying a 300 dollar set of Copic markers-- depending on the online store, you could get back up to 20 dollars.  Personally I use Dick Blick Art Materials.  They have a large selection and have low prices.  As for specific pens, you can get professional ones that are used by designers like Scott Robertson from JetPens (Japanese Imports)-- rumors say he uses the "Hi Tech C Gel Pens."  They come in various sizes however if you want more control over your line weight you shouldn't get anything below 0.4 mm.