Bleugh... Knew this thread would get full of boring 'step sequencers suck just use the SP better' replies. Using a step sequenced sampler's is as good as any other sampler, it just comes down to your imagination & ability to make a song. Personally I find putting together rhythms much faster in my ESX than SP (of course that'll vary person to person). Why enter one sound per play through when you can program all hits at once? It's not finger drumming, but it's not to be underestimated. Plus if there's a slightly out of time drum you can fix it immediately- not the next playthrough. If you want to make your drums sound loose & unquantized there's tricks to make that happen (record silence before the drum sound plays, automate the start point of the sample in the motion sequencer). It also helps to understand how to use swing & accents effectively.
Earwax, you're probably right about the ES being best for your needs. 2nd hand the ES & 505 go for about the same amount too.
Even though this tutorial's for the ESX, you can do the same thing on the ES:
http://www.youtube.com/watch?v=lGctUPri1ewThis method shows how to save multiple drums into a single sample slot then play any drum from that slot like it's the only sound available. It's like turning 100 sample slots into 1000.