Yeah I don't wanna be harsh... just realistic. But I think if you really set your mind to it it's definitely not out of reach. I do know that it seemed a little easier in my head a while back. I'm not sure what the currency amounts are on Aegis but here's what it is on Gjallarhorn.
Stage 1 -> Stage 2 (300 currency)
Stage 2 -> Stage 3 (1,400 currency)
Stage 3 -> Stage 4 (6,000 currency)
Stage 4 -> Stage 5 (10,000 currency) = 17,700
Now on my server atm currency is around 30k more or less. Let's apply that.
1 -> 2 (9M gil)
2 -> 3 (42M gil) = 51M gil
3 -> 4 (180M gil) = 231M gil
4 -> 5 (300M gil) = 531M gil
Now let's assume that you managed to get in a position to sponsor every single run and at every single run you got 300 currency. (this is beyond unlikely as your shell will probably split sponsorship and getting 300 every run will be impossible because you'll be doing ice) This is just a for instance.
So me working on my Horn and needing 17,700 currency.
17,700/300 = 59 runs
59 runs/2 runs/week = 29.5 weeks
29.5weeks/4 week/month = 7.375 months
That's over half a year under the absolute most hospitible conditions of having a shell that is working just on you. Now my shell currently has a rotation of 3 sponsors. Other members can bid their points to lot 100s (including those sponsoring) so sponsors don't get all of the currency. I think this is how a lot of shels work to keep people interested.
Now 300 currency isn't impossible by any means and makes for a decent average. We do do ice or CoP dynamis' one out of every 2 days of the week. Essentially each sponsor is sponsoring on average one day out of every 3rd week. So let's look at it like that.
52 weeks/year
52/3 = 17.3333 sponsorships a year
59 required sponsorships/17.3333/year = 3.4 years
So under normal conditions and not using any other means to get currency I could get my Gjallarhorn in 3.4 years for only 59M gil. Obviously most people who have a Stage 5 relic find other ways to supplement their upgrading.