Welcome to the new world of lipo and brushless
You can get away with a couple of cheap-ish stick or saddle packs, depending on your chassis config.
You will also need a lipo-specific charger (£20 ish) and charging sack. You may also need a personal transponder, but the club you end up racing at might be able to let you hire one or buy cheap.
Your best bet by far is to join the BRCA & find your local club - go along and ask for advice there. You're guaranteed to find some cheap second hand kit.