No truer truism for this - buy cheap, buy twice.
I'd avoid a bass starter pack - the amplifiers will be under powered and lack tone which will have a negative impact on your motivation.
Lots of decent amps producing 50w plus or keep your eyes open for a Trace Elliot BLX80 or 130 combo. Both much louder than the numbers suggest.
They can turn up for £100 - probably the best money you'll ever spend.
Lots of good advice about entry level basses above - I'd also add Yamaha BBG4 - I picked one up for under £100. Lot of bass for not much money.
If you're in the Herts area you're welcome to pop round and try some gear.