I have a D2, and it has one moveable condensor just below the light source. I don't know the size of it, but at the lowest shelf, it sits down into a hole.
For a 150mm lense, you take it out altogether, for 50mm it goes in the bottom shelf (If I remember correctly), the door to the chamber tells you what to do with which lens.
I went with the D2 for the same reasons you state, wanting 4 x 5 capability at a reasonable price. If I remember, I picked it up for around $150. I don't know the specifics, but I bought the enlarger, a Kearsarge digital timer, one Componen S 50mm and one Componen S 150mm lens for $350 at a garage sale.
I had been watching Ebay and seeing about those prices, but lucked out not having to deal with shipping etc. Good luck. If you get one and need manuals etc. I think I have the digital files some friendly folks provided to me.