I custom built a PC which was pretty cheap cuz I was sick of producing on a old 2ghz duo core with 1gb ram laptop from 2007 or my old desktop with 2gb ram and ... pentium 4 1. something ghz processor lol.
I got a Gigabyte motherboard bundle, a i5 760, 4gb ram (i have a extra 4gb but it doesn't seem compatible with my MoBo), good soundcard, decent graphics card, PSU, keyboard/mouse, etc for like 600 and a 24 inch hd monitor took it up to 750. I can 'so far' run pretty much anything I need. I haven't had to freeze or bounce tracks yet and i've had some huge L.A.S.S/Omnisphere uplifting trance projects with like 10 vsti's playing at once with no problems yet.
i was gonna go for a dual monitor/i7 980/12gb ram beast machine but tbh i'm glad i halved the price cuz so far I haven't needed anything more and when/if i become more serious upgrading is always a option..