No problem Alex, with regard to the £25 that I believe is just for the isa account. So yes, that said £500 I can't see a return taking you over your CGT allowance for the year so I'd stick with the traditional account. I can't see any cheaper way of purchasing the shares..iweb are the cheapest I believe. You can get one (I forget the broker) for 4.50 or 4.75 but they charge a quarterly inactivity fee.
anyway, good luck with that
the alternative I had in mind, was formerly Gecko (now ayondo) which allow you to spreadbet without any leverage/margin so you don't incur any overnight charges. For your timescale, that would have been ideal but they are limited in their products. If you find something else, you could check with them to see if you can trade that stock.
Post edit:it seems the 25 is for the traditional account also (which sucks). apologies for that Alex. however advice still stands if (and thats a big IF) you were indeed hellbent on RDT. personally, I look to buy things that are on the way up, rather than down but that is just me and my philosophy.