My path went something like this, these tabs are out of production except for the last but you get the idea. Wacom Graphire 4 4x5 $99 retail > Wacom Intuos2 12x18 $200 2nd hand > Wacom Intuos5 Large 8x12 $350 retail + wireless kit $30
I dont find the current gen intuos pens all that comfy but that's all personal preference. Luckily you can get different pens on the intuos lines \o/
Back on my intuos2 I used a Classic Pen for linework and the Grip Pen for shade work, these pen types are still around but probably under different names I also bought another Classic Pen for just osu! because I found that vigorously tap playing osu! eventually degrades the pressure sensor. This was all back on my old tab I no longer play osu! on my current tab because 100 bux a pop for a pen im not going to find out if the design was made more robust.
Id look for 2nd hand intuos 4 or 5/pro medium... You'll want more active area