About the installation, well once Koha 3.0 is ready there will be a Koha-KOS CD [ probably Brooke will write about it so watch this blog if you are interested] which will install Koha in 15 -45 minutes [ depending upon your machine specifications ] straight. This I hope will help cut your costs on Dr. Pepper or Jolt :).
As far Hardware is concerned that depends upon the quantity of articles and circulation. IMHO the prices are rather high, I would recommend buying some OEM made Linux Based machine [ CPU only ] it will work fine. BTW what you save do not spend that on Pizza party rather spend that money on UPS [ Unintruptable Power Supply ]and connect only CPU and modem / router nothing more.
There are NO training costs which are Open Source specific. If one is willing to read then they are free while in case of commercial software there is nothing free even if one is willing to read and learn.
With the exception of Hardware if one is willing to invest time then there is NO NEED for money, except for eating and living :).