As for the DAB option, I hope you've got a hell of a lot of money.
Actual digital licenses cost a few hundred pounds however carriage (with the multiplex operator) can cost £10,000s depending on how well you can haggle. There's then the usual music licences, etc.
Bridge FM, Heartland and RNA time-share on the access channel. I've got a feeling we would not be able to get in on that agreement as a cost reduction measure.
The coverage from the top of the union on previous RSLs was good for most of the town. However, there were certain pockets of poor coverage (e.g. Gatty / Albany Park). The single site restriction was the reason I didn't suggest it was a good site, not coverage of the town. We would not get a licence for a single building as for long term RSLs we cannot recognise any audience offsite. The quad / library area could be another contender if we could define a continuous "site" from the various university buildings.
As for low power AM coverage, take VRN (Kirkcaldy as an example). The signal is good well into Glenrothes and occasionally listenable in Dunfermline. They've not exactly got the best site in the town either...
And for all out roundness... commercial licences are out of the question (Ofcom ain't advertising them any more), satellite costs way too much and we have to wait for the next round (if there is one) for a community licence. Though on the community one, we'd have a hard time proving St. Andrews has a community neglected by the commercials.