How about the Jolida JD1501a Hybrid at 100watts per channel it should be adequate for your Advents and still give you a taste of tubes at a reasonable price. Most of the comments have been positive and it might be worth a look. I don't think you will be able to find a pure "tube" amp in your price range that will be able to drive your Advents unless you get a real deal on a used amp. But good luck in any case.
Regards,Jerry
Regards,Jerry