I imagine the costs of an EPG
slot are a tiny fraction of the costs of actually getting the channel to / from the satellite. One requires a significant amount of hardware and access to a limited number of resources, and the other is an entry in a database. I doubt very much that deleting a couple of rows from the database would free up enough cash to pay for even one grand prix / six nations match.
In the case of the regional/national variants, all the data still has to be there anyway, so you're literally only talking about the cost of a channel number, up in the 900s, so very little resell value for anyone, to the point where it's probably has a positive result in a cost/benefit analysis from allowing people from around the country to watch any of the channels.
There is one factor, you've not considered, it's the 'regionalisation' fees that BSkyB charge the Beeb. You're quite right, basic EPG inclusion is trivial, compared to all the other costs, and those costs are regulated by Ofcom. However, back in 2003 when Greg Dyke declared he wasn't going to pay BSkyB's encryption costs anymore, and announced that the BBC would be moving from being encrypted on Astra 2B to unencrypted on the 'UK narrowbeam' Astra 2D, at the same time he said that all 22 or so BBC 1 and 2 regions would be available, and available UK wide. For that to happen, BSkyB had to provide a 'bespoke' regionalistion service, basically to map to Ch 101 and 102 the correct region for a given registered postcode. The cost of that, is not regulated by Ofcom. The Beeb have never publicly stated what they are paying for that service, but it's thought by some to be not far off the original fees they paid pre 2003 for encryption. ITV of course have the same service, and in fact initially the same postcode database was applied to the BBC, which is why for the first few months, a few areas had the wrong BBC 1 region on 101. ITV have never stated what they pay BSkyB for that, again those costs (over and above basic EPG inclusion) are outside of Ofcom's jurisdiction.
Of course, none of that applies to the Freesat platform, which the Beeb are major stakeholders in.