All of the models have pretty much the same likelihood of being available with a manual transmission. The 320 (2.0l, not avai;able in the US),323 (2.5l), 325(2.5l), and 328(2.8l) have 6-cylinder engines. I would recommend that you get either a 328 or a 325, since they are faster. The 328 has the most torque among these two, but the 325 is easier to mod because it is OBDII. Run a search. There is abundant information regarding this issue here. $7500 should be enough to get any of these in decent shape.