yes its fairly cheap and easy enough to do , i've recently done this myself to make a range of small animal figures. for my design i made lots of the base figures from the mould and then hand worked each one individually and uniquely so even though they came out of a mould each one is still unique......
tips i learn doing this are;
1) stir your silicon or rubber gently and if possible on a vibration table to limit/pop the bubbles that will spoil your design.also pour it gently.
2) be careful how you shape your design your figure beware of sticking out thin bits like ears and legs etc as i just kept snapping them off trying to get them out of the mould and it drove me crazy.
3) depending on what medium your using to cast you might want to make a few moulds as some mediums like resins can take 24-48 + hours to set and if you want to make 20 and only have one mould you'll be there forever
4 be patient one of my main problems was being to impatient to wait and taking things out of the moult before they had set
5 check check and check again you have you mix ratios correct esp with resin otherwise it can fail to set, EVER and remain sticky and a waste or be too brittle etc etc
there are probs more hickups i encountered along the way that would have been usefull to know before hand but this is all i can think off on the top of my head, hope its useful to you x