[acropolite (Phil)]

Mischa, a dob requires very little maintenance and aside from having to take it outside some time before observing to allow some cooldown time it would be easier to set up than an AZ3 mount. As the others have said, anything around or under 100mm will not have much resolving power, 8 inches (200mm) is about the minimum I would aim for.

If you're going for an Alt Az tripod type mount then either the Vixen porta mount or the GS copy will be better than the AZ3 as they have a balanced mounting arrangement and slow motion controls that work over the full range of movement (unlike the Az3)
The Az3 mount is poorly balanced; it has the OTA above the alt pivot point and the OTA tends to topple if the friction adjustment isn't set just right. The slow motion controls on the Az3 are limited in range and have to be frequently reset. I bought an AZ3 mount, used it once only and immediately bought a porta mount to replace it. The GS clone is of the porta mount is available (mount only) for $249 at Andrews I believe. The GS item, despite having sturdier legs is not as rigid as the Vixen Porta IMO.

If you really want a portable setup with a good useable mount, then you can't go past the Porta mount newt combo that Geoff (starkler) recommended, even though it will cost you a couple of hundred over your intended budget.