You can spend as much or as little as you feel is necessary. Cedar shelves or trays are not at all necessary but many like the look. With my second Vinotemp I chose to use the wire shelves as it is mainly for box storage, I use empty boxes to hold singles. In my first, I added cedar shelves by cutting 4"x1/4" cedar planks(Woodcraft). I used two pieces per shelf and left about 1-2" in between for air flow.
I also use 1lb of Heartfelt 65% beads in two bags, one on the top shelf and one on the bottom.
The biggest problem with a condenser fridge is raising the temp to an acceptable range for cigars(60-70degrees) for this you will need to connect an external controller such as those made by Johnson Controllers.