They are just a 'train operating company', don't think of it as a line closing.

You say you are getting fares of £69 upwards (which looks like an off peak single for this route), just checking, you do know that the way train fares work a return is usually only a couple of pounds more.

Indeed, the off peak return (which can be an open return - so you can change your return travel time) is only £70 (so effectivly £35 each way, despite the same type of single being £69).

The only fares you will get cheaper than that are discount advance fares (and/or split ticketing).

Are you wanting to travel actually on the Friday (20th) and Sunday (22nd) themselves? Or be in Wrexham for thouse days? What time do you need to be there?

Looks like there are advance fares available on the route from £8 upwards. However I can't see any availability on thouse days.

Deeply discounted advance tickets are subject to allocation restrictions, and advance purchase requirments, are quota managed, etc.
Also, many deeply discounted tickets are frequently only valid for direct (no change of trains) services.

On the outbound, the only Advance tickets I can see are for the direct 18:10 > 20:39 Virgin service for £30.50. [This seems to be the only direct serivce to Wrexham.]
Of, if you want to arrive later and add another hour to your jouney, and two connections: Virgin from London Euston 20:43, connecting Birmingham NS to LMS to Shrewsburry connecting Arriva to Wrexham 00:14 for £17
On the return I can't seen any advance tickets on the Sunday.

Personally, I think you will find it hard to beat the £70 off peak return - especially for easy of use if you are new to the UK.

Apart from some very special promotional fares, all normal fares can be booked on any train operating company site.
I like the interface used on the east coast site myself, others also have this interface:
www.eastcoast.co.uk