What about a Pontiac G8 GXP 6spd? They can be had for $35K with rebates. There are tons of performance parts that actually add power. You could mod the hell out of it and still be well under your budget. Size which is roughly the size of my 03 Altima which is not that bad. My cousin traded her 06 325i 6spd in on a 08 G8 GT because she was sick and tired of have to drive over an hour for service. Its awesome to drive and its handling is on par with a BMW. Hell auto rags call it the cheap man's M5. She has already done intake, cat back exhaust, software, and lightweight rims. Its making over 400hp. Her dad owns a 01 BMW e39 Dinan M5 that the G8 will keep right up with in the straights and corners. I would buy one if I was in the market for a V8 sedan.
There are acouple more modded BMWs in my family besided the M5. One of my cousins owns a 04 330i ZHP that has every part from Turner Motorsport bolted onto it and a AA supercharger. And his brother has a 07 335i coupe 6 speed manual with the factory sport aero package. He has performance software from TMS makes (+40hp over stock and +39lb/ft of torque over stock). That’s 367hp and 372lb ft of torque. It also has a BMW performance short shifter and knob, Borla cat back exhaust, AFe dual CAI, AA larger intercooler, AA blow off valve, and LSD. With the software, cat-back. and CAI its close to almost making 400rwhp. He is talking about doing the BMW Performance Suspension Kit with includes struts, shocks, springs, and larger swaybars, BMW Performance Steering Wheel, and Carbon Fiber Interior Trim. He has alot of money tied up into this car.
Let's just I am jealous but I do get to drive them.