I don't know anything about your other thread, so this is just based on what you've said here. If he's old enough to have a grown son and he just got evicted from a place he was renting with a roommate, it seems possible that he's got some issues which would affect this decision. That said...
If he was anything but the most horrible or deadbeat of dads, if he's got his act decently together (doesn't shoot smack, start a lot of fights, etc) and if you don't desperately need the money, I'd say let him stay for free. There would have to be a REALLY good reason to accept rent from your own father, especially if he's disabled.
Unless there's something important we don't know, him charging you rent when you were 18 is NOTHING like you charging him rent now. Generally speaking, it's actually a parent's duty to require their kids to start contributing to the household finances at a certain age, which would vary by situation. If they don't, they're not teaching you how to grow up and get along in the real world. By contrast, if he wasn't the worst dad in seven states, you owe him a huge debt which you can never repay.
It doesn't always help someone to hand them something, which is what the first paragraph is about...would you somehow actually harm your dad by giving him free rent (enabling his alcoholism or something), or would it keep you from fulfilling other very important responsibilities (like if your dad constantly picks fights with your wife, or you're way behind on your mortgage and need to rent the room before you lose the house)?
If not, let him stay for free, have a good attitude about it, and request that he do the same. Being a man isn't about what you can get away with, what you're owed, how well you've been treated, or how much you can justify yourself...it's about doing the best you can do and being the best you can be.
If you're not willing to follow that advice- charge $250. Include utilities (life's too short to haggle over this stuff, especially with family), but request that he conserve. Also let him know that this will be fairly modified if your utilities change and it affects him. If you spend $30 a month on a new movie package, ask him to pay $5 more unless he absolutely never watches it.