Some times before I found on http://irieelectronics.de/diy-meeblip-anode/ and http://www.instructables.com/id/DIY-Mini-Bass-Synth-Meeblip-Anode/ the clone of the Arduino Bass Synthesizer, MeeBlip Anode. It is open source and easy to build. The cost will be about € 40,- if you order the most parts at chinese suppliers via eBay inclusive the enclosure and all accessories.
All parts are are located on a stripboard. The poties and connectors are placed directly on the enclosure and wired.
The enclosure is consists of 3 mm birch-plywood:
2 piece 120 mm x 84 mm
2 piece 120 mm x 120 mm
2 piece 120 mm x 34 mm
2 piece 114 mm x 34 mm
The screwed joints for the cover are made with distance sleeves.
And here 2 modre pictures of the finish synthesizer.