If they can't afford to pay a market salary, you should be getting at least 0.5% (and probably more like 1%). Still not life changing at 40mm with no dilution (200-400k), but a little more meaningful.
Most of the YC companies seem to be favoring "large seed" rounds, which are at levels that might have, in recent years, been more appropriate for A rounds. The $6mil seeds, and such. That probably leaves them in a position of: a) not a lot of equity left to spread around b) it's a seed round, so there's little to no revenue coming in yet, which means they want to hold onto as much of that cash as possible. Depending on how the deal was done with investors, they may have such a small options pool that you're never going to get the 1% you want, and yet they also are not going to pay the $100k+ you are worth. What they are offering you is the "prestige" of working for a YC company, and it's your call if you think that has future value for you or not.
Now if you get hired by one of these and they make it for a few more years, and you stick around, your salary will likely go up significantly and additional options be granted (though you'll probably need to make an effort to ask), but I wouldn't count on getting life changing equity out of any startup if you're joining after they've raised 7 figures or more.
If you're a non-junior engineer, and one of the first ~10 employees, this is fairly common. At least at the point of issuance; 2-3 VC rounds reduces the percentage (but increases the value, at least in theory).
Now if you get hired by one of these and they make it for a few more years, and you stick around, your salary will likely go up significantly and additional options be granted (though you'll probably need to make an effort to ask), but I wouldn't count on getting life changing equity out of any startup if you're joining after they've raised 7 figures or more.