You are looking for option X "today", tomorrow you will look for option Y and then Z. Believe me, the cheapest option is a shop built on the EXT version. There are already XYZ options :)
I know that's better start with EXT version, but this lady doen't want spend much money (255 EUR), when she doesn't know how her small business will go. She's on start now. Are you do this? I think, that you are one of them, who is able to do implementation like this.