I have to agree with Buddy here Graeme. As much as I love Maicos, 250s aren't the most exciting bike in the class. As good as Maico open classers are, the 250s are as dull as dogshit. The best open class pre '75 er is the one you like best. CZs are good value, Maicos are fast but expensive to buy and maintain, Huskys are great bikes but expensive for parts, TM400 Suzukis need settling and are trendy right now for some obscure reason, Yamaha MX360s are good honest bikes, reasonably cheap to buy (if you can find one) but need serious suspension work and Bultaco 360s fly but are fragile. My pick would be Maico 440/400,Husky CR400 and Yamaha 360MX. In the end though it doesn't matter what you buy as the bike is only going to be as good as you are at riding it. Buy the bike that gives you a fatty.
Unfortunately the window of opportunity of getting USA bikes for near parity pricing has closed with the OZ dollar stepping back to 88c. I've recently seen 2 400 Huskys for $600, a 360 Pursang for $400, a TM400 for $900 and a pre 65 Triumph for 2k in the USA. When you add the $1000 to ship it here you're still in front compared to our prices.