Since my name has been brought up I thought Id throw in my 2 cents.. Quality materials have been mentioned already so I wont get involved there. what I will do is list a few pros and cons of doing them yourself.
Pros.
1. Make your own unique design.
2. save a little money.. Not lots until your casting 100\'s of bases though.
3. satisfaction of doing something on your own.
Cons.
1.Even for small amounts, Expensive. Your looking at about $50-60.00 in material costs to get started. For things like resin, rubber, mold release, mold box materials and so on.
2.. Messy.. trust me Ive ruined more clothes in the last year casting resin than I care to think about. so wear old clothes as you will spill.
3.Time consuming. from sculpting, molding, casting your looking at quite few hours time. Takes me 30+ hours to get a set to market. What is your time worth?
4. Materials have a shelf life, once you open them and start exposing them to air they go bad. For resin 30 days tops especially for your B side. So unless you invest in a Nitrogen Purge..another $15.00 your resin will go bad in 30-45 days or less. Your rubber has a shelf life of 6 months to a year.
5. Unless you have the equipment to Vacuum or pressure cast, expect air bubbles..
6. Clean up and disposal of waste materials.
Anyhoo just thought Id toss my thoughts in. If you have a friend who can make molds and help you then you may have 1/2 the battle over.