Do not forget that the number of missions itself is limited and a limiting factor in deck construction. There are missions that allow downloads mission IIs, like
Visit Parallel Universe -- which has a pretty similar cost to missions IIs in that you have to seed a fairly low point mission.
There are also cards like homeworlds,
planets that let you download an emblem card and spaceline locations that correspond to time locations that provide free plays. All of these which other than
Police Trade Route, which caries an implied cost of being a 40 point mission your opponent can attempt using any
personnel, are planet missions. You are limited to at most 4 planet missions in most decks.
For the cost to be similar to a mission II, the card itself would have to be a mission and it couldn't let you download ANY card. This is why I liked the proposed card from the 2024 March Madness that let you download a Shades of Gray card.
If you want a card that is -5 points and seeds free, I would go with something basic like a an
door. Remember, when Au door was released the "30/30 rule" -- limiting players to 30 seed cards -- was not in effect yet. Thus, there was no additional "cost" just to include cards from the new set in your deck. (And hence the crumminess of many early dilemmas -- you were not limited in principle to any specific number of them.)