As previously stated, there are a few customs made by certain artists that seem to go up in value (Rainman, Serang, etc...). There are also some customs that are just pieced together by board members that can fetch a pretty penny as well (depending on what items are used such as head sculpts, type of clothing/accessories). Some hot toys/enterbay figures still carry a decent value but I remember when the HT Iron Man mark I was going for $400+ at one point but since it has been reissued (with better quality), the originals are not carrying as high of a value. Then there are figures like the HT Harvey Dent/Two Face. I got one when they originally came out and then got a second one in like-new condition for $100 a year after it came out. Now people are asking $300+ for it. Just dont think about the prices of your figures. It just helps in enjoying them. I will say there is a certain amount of satisfaction and happiness you will feel when you walk by a shelf with custom figures on it. Just knowing you may be one of only a handful of people who have one worldwide as well as the character being a favorite (i hope your customs are favorites as the prices for customs tend to be high in the first place) should provide a good happy feeling for ya. God knows I crack a huge smile whenever I glance at my Rainman Dude or PeeWee or my custom Wormwood Gentleman Corpse figure. Good luck with your collecting and welcome to the community.
Just remember, whenever you decide to get a custom, whether you put it together or its done by someone else, make sure you get EvilFace or Corrose to do a custom stand decal for ya. It adds so much to it all.