For one thing - a 2.5mt rated commercial jump drive at the lowest base jump drive efficiency of 4 only costs 2,500 duranium and 10,000 sorium according to my version of Aurora (current) - which, isn't nothing, but is still only a third of what you mentioned. Are you sure you aren't accidentally using military jump drives unnecessarily? At this lessened cost, it might make sense then to create a station (no armour) with the 2.5mt civilian jump drive as the only component and tug it to whichever jump point you require, though I would recommend against tugging such large stations into potentially contested territory in the first place.
Personally, my stabilization ships are in the first wave that I send to any system where I am planning to found a major colony, alongside whatever I deem to be sufficient initial defenses. "Sufficient defenses" could mean a fleet in orbit of the most promising body in-system and sensor buoys at every incoming jump point, or it could mean a fleet stationed at the jump point itself using recreation and maintenance stations (especially handy when hostile contacts could threaten vulnerable stabilization ships), or it could simply be a naked stabilization ship in a quiet, empty system that I don't expect to have any trouble defending (I have been punished for this reckless overconfidence numerous times). But the sooner I can switch from precious government shipping to civilian orders (which require a stabilized jump point), I do so. Using the small stabilization system which can take up to a year, this usually means stabilizing in advance *during* the colonization phase, when my government ships are going in and out. As long as I have the forces to spare, I go for it ASAP. It's my territory, after all.
Very general potential spoilers: Generally, I have found that hostile forces will either be fully capable of supplying their own jump ships for an assault, or they aren't interested in crossing jump points in the first place, so stabilization doesn't actually make that much of a difference in the security of the system IMHO.
I am an incorrigible save-scummer though, so, maybe my advice isn't the best advice to follow!