if it isnt cheaper it will be soon.
aaisp's prices have been fairly static for some years, they dont rip you off on line rental either.
meanwhile BT have inflation busting price rises every year sometimes twice a year.
On the 100gig allowance, it can be seen as a bit out of date, but clearly aaisp are getting enough customers with it or else they would have changed it.
AAISP prices are related to their cost, they dont give out retention deals etc., their costs are higher than BT as they dont have the sheer customer count to drag it down and they also use a more expensive way to get backhaul. Of course also they cannot cross subsidize.
Within a couple of years I expect line rental on BT will be double the cost of aaisp.
As for extras on BT they mostly useless, evening calls? (no thanks got a mobile for calls), wifi (in my area I was the only wifi transmitter, at my parents is none there either so useless), BT sport? ok but depends on the customer, cloud space? I did use this, but there is free alternatives such as dropbox and google drive.
Also the average user uses way less than 100gig a month, if they didnt then prices would be higher than what they are now. The likes of BT can sell unlimited at their price point because they have millions of granny type users who use about 100kb a month.