Cheap silocone casting resin (1 or 2 component resin)?
The problem with attempting this is the nature of the cheap silicone.  Most store bought silicone is already polymerized before use.  For example, the silicone caulk which can be purchased in home improvement areas is a finished product which  has been infiltrated with solvent.  These caulks contain no catalysts to facilitate reactions.  Any curing is the result of solvent drying from the caulk and solidifying the resin.  

If you were to attempt to further dissolve one of these materials with something like ethyl acetate (see here for a simplified list of solvents), it probably would not go well.  All you would be doing is further impregnating the silicone with solvent.  While this would decrease the viscosity, it would increase your drying time.  Shrinking would occur during your casting, and I expect that you would also experience a very messy result, no matter the quantity of release agent you applied.

Consider a very simple silicone (aka polysiloxane).  Two silanol molecules react by hydrolysis to form a disiloxane and a water molecule.  In order to reverse the process and obtain your starting material, you would need to put the water back into the disiloxane to cleave it.  This is energetically expensive.  

Even the full polymerization process is not a spontaneous one.  When you purchase a silicone casting resin from a supplier, you are actually buying a Part A composed of n-siloxane (where n is a small enough number to be a liquid) and a Part B composed of crosslinker and catalyst (this is often silicic acid and tin because they are inexpensive).  So what you are actually doing is taking a short chain polymer and crosslinking it into a solid mass.

Adding silicic acid and tin to a store-bought silicone product such as caulk would probably cause a reaction.  The result would probably be a very hard rubber with incompatible properties for casting.  However, I have not attempted this.  Furthermore, I am not sure silicic acid would be easily accessible to a home chemist.

Despite how fun it would be to synthesize your own silicone casting resin at home from everyday chemicals, it probably isn't feasible.  There are some inexpensive options out there for resin casting, and I encourage you to go with those.