hmm, if you shop smart you can snag a spark and d10 together for around… I want to say $150, 58x jubilee is normally priced at $150, and a modmic(probably usb which is the better one) at $50(or you can actually get a blue yeti at $60 if you luck out) putting it right at your $350 budget.
As for where? Head-fi, Amazon, Ebay, Buy/Sell and Looking for Thread - #222 by LeDechaine here on the site, https://www.reddit.com/r/AVexchange/ here on reddit, USA Audio Mart, and lastly https://www.hifishark.com/ can scour multiple sites for a deal by typing in the item name in the search bar.
I should add, going to third party sellers… always use Paypal with an invoice so your protected financially and make sure they have photos showing the condition of the item and a little card showing the date and their username which proves ownership. Gives you security during sales