All spending bills must originate in the House. Obamacare was started in the Senate by using an appropriations bill already passed in the house, and amended it by striking every single word out of the bill, including the title, and amending it with the Obamacare bill language.
I thought about that, but it's really not a "spending" bill, it's a "cutting" bill. Don't know if that makes any difference...
If I recall correctly a bill was already passed, just not funded. If that makes a difference? Also, no reason the Senate cannot propose a bill, the House takes the text and passes it first then it goes to the Senate for passage.