How 'bout an air suspension Turntable shelf...? Cheap too.
Brackets: 1/4 inch steel flat-bar from Home Depot. size is 18 inch.
Stud Finder: Home Depot, again. Electronic stud finder less than $10.00.
Bolts: 3/16 x 2-1.2 inch lag bolt. (6 used. 3 each bracket to tie brkt's to studs behind sheetrock.)
Carpenters level for getting shelf level.
#10 Wood Screws to secure lower shelf to brackets.
Shelf mtl.: Grade A Birch ply, 1/2 inch thick.
Inner-tubes: 3 hand truck inner-tubes from Home Depot (again..)
Blue Tack: between brackets and wall, brackets and shelf
Fabric Covering: optional. I've got green leather (cowhide) here. It would be possible to construct the top shelf with side covers and a laminate surface texture of your choice. Many options.
1) Proximity to room corner makes tonearm/cartridge susceptible to standing wave resonance. On the other hand, the corner offers best possible structural integrity of supporting wall studs. A compromise.
2) Recognizing that the brackets and plywood by themselves would not provide optimum isolation from surface borne vibrations off the wall, I added the inner-tubes and a second shelf to isolate. This did result in an audibly quieter (blacker) background.
3) Added benefit: One can set level of top layer by altering inflation of tubes.
4) I inflated tubes with a very low air pressure to make them a more compliant springing medium. Higher air pressure would have firmer suspension. A bicycle pump works fine. A small portable compressor is even better if you're lazy like me.
5) It would be entirely possible to inject liquid (using a syringe) into the tubes in addition to or in place of air for a "different" damped spring compliance. I've heard of people using vegetable oil. I haven't tried this, but it remains an option. Leaks could be catastrophic, however.
6) Variations on shelf material could be used; acrylic, Corian, tempered glass, marble, various composites, etc. I priced acrylic at 2 inch thickness for the above dimension at over $300 one plate.