Remember, the basic income is taxable. Giving the basic income to someone earning, say, the equivalent of 100k USD doesn't actually mean giving them $33600, because it will all be taxed at the higher tax bracket. People will also buy things with the basic income, incurring VAT, and if they buy Swiss things, then the companies making them will also pay corporate tax on that.
So, yes, this programme would cost _something_, but it wouldn't cost 34% GDP.
I'm a big fan of basic income, and politically very much a leftist, but I also think basic income goes very well with a flat tax rate.
If you consider progressive taxation as a high tax rate with a discount for lower incomes so they get enough money to live, then basic income, which provides enough money to live, can replace that discount. Just like it replaces welfare, unemployment benefits, etc. It's going to make social security and the tax system both a lot easier, and cut down a lot on bureaucracy.
So, yes, this programme would cost _something_, but it wouldn't cost 34% GDP.