The cost of a *A RTW ticket depends on three factors: where you start/end the trip (the origin and final destination must be in the same country), where you sit in the plane and how far you travel. The *A Special Economy RTW (aka Star Lite) is, as the name suggests, only available in sardine class. It is also only available in selected countries; the UK is one, but Ireland is not. The distance limit is 26 000 miles. Your proposed itinerary is well within that limit. Beyond 26K takes you to the first of the regular RTWs, with a limit of 29K. (It is available in all three classes, but you say that your work won't pay for anything more than economy.)

The UK is a good place to start an economy RTW. The base fare for a Star Lite is £1259, with the 29K YRWSTAR1 at £1480. In comparison, from Ireland, with no Star Lite, the cheapest fare for any itinerary up to 29K is €2519, or almost 2000 quid. So, to go back to your 'The LHR could be replaced with DUB if that makes a difference': you probably don't want to do that.

If you go to the main Star Alliance website, you will find a tool called the *A Round the World Mileage Calculator. There is both an online and a downloadable version. It has some bugs but in general it is very handy and great fun to play with. One thing it can do is help you stretch your itinerary to 25 999, the better to fulfill your wish that 'this trip will push me into Silver'.

One final note: the *ARTWMC will give you the base fare for your itinerary, in accordance with the three factors I outlined above. In addition, there will be taxes and surcharges of several hundred pounds added on. The only way to know the exact final price is to construct an itinerary and submit it to the rate desk of a *A carrier for calculation. The *ARTWMC also includes a mechanism for that purpose.

Good luck.

cheers,

Henry