Hotels are going to be what you can find them for, modern cheap hotels i.e. holiday inn, premier inn etc are likely to be the most basic and clean, a lot of the cheaper hotels are older and touristy, Victoria has a plethora of cheaper ones, under £10 in a black cab.
Personally I"d only take black cabs when in town, even if I drove into town I would look to leave the car at the hotel (if available) and use public transport to the venue, the Vic car park is quite small, parking locally is expensive, meters are about £9 an hour. Oh yeah don"t forget, if you drive in to town and arrive before 6pm on Friday or leave after 7am on Monday you have Ken"s legacy to satisfy, we have the congestion charging zone, you will have to pay £8 for the priviledge. don"t pay and it"s £70 to start and it gets even more expensive after that!!!
Check out the Transport for London website for details of the charging zones. A bit of shopping in Oxford st is car free only buses and taxis allowed.
Ha! welcome to our life. Have fun.