I am not suggesting you buy from Harry as his prices are high and you can get most of what he has for half to a fourth what he charges. Just mentioned him as a source of info and hard to get parts if necessary.
As for lens cones you can get away with a 2.5" for your 105mm and even use it with a 150mm which is what I do. The only downside to this is that you can't print a 4x5 neg smaller than about 6x8 inches. I have never wanted to so I haven't gotten the 4.5 cone recommended. A D2V (for variable condenser) is a lot easier to use enlarger if you change formats often, but it will cost at least a $100.00 extra. If you go for D2 (not variable) make sure you get at least the 6x6 and the 4x5 condensers as they will cost you an arm and a leg to get later.
Two suggestions, check out local used camera stores for whatever you decide to get, and try to get a package with most of the accessories you will need. Ebay is an option also, but prices around my area aren't much higher and you get to personnally check out the unit locally. Shipping on Ebay can also be quite high as I have seen some shipping charges as high as $75.00 added to whatever the bid price is. If the enlarger turns out to be garbage you have to pay for return shipping even if seller will refund. Check out a recent thread in Photo.net with this problem.
After all that I have to say there are better and easier to use enlargers out there for 4x5 (or so I am led to believe) but I doubt if you can find better for the price used and your initial question included the word CHEAP.