Offering dev time is very hard, but as someone who has worked in industry for so long, we can definitely help with guidance and advice.
To be clear, that's an easy 2mm valuation. That's also an incredibly tiny slice of the company, and that's also something that will get diluted to shit.
So, let's stop this meme that for an early-stage company that fractions of a point are somehow a big deal. That's how a lot of early employees--who do the hard work--get screwed.
If a startup is valued at $2mm, they don't need your measly $1k. To make that worthwhile they would need to get $1k investment from dozens of different investors. And at that point they're no longer giving up "only 0.05%." Also, if they need an advisor, they can find one. If they need a contractor, they're not going to pay via shares, because the whole point of issuing options/equity is to align the long term incentives of the startup and the investor/employee. A contractor does not work long term, so there is no need to give away shares.
Also, the suggestion of the OP -- a place for investors to get advisory shares in companies -- already exists. It's called Angellist.
If you are truly investing in a company, dilution is irrelevant. The only two things that matter are share price and your ability to liquidate those shares. If I buy at 1-cent and sell at $1, I could care less about how much my original 0.05% has been diluted.
What YC brings to a startup for their 7% is 120k + advice + connections + the YC brand itself, so just 1k will be worth only a fraction of 1/120*7% of the company (I'd say, about a half or a third, maybe even less).