ALTEON is a Boeing subsidiary, and they have a large option on solutions. I had to research for training on B737 (not NG) for a company i worked with before, they ended up taking Flex in Rio, but wasnt the best or cheapest option, it was rather due to the fact of the crews poor English...
There are many providers worldwide LHT e.g. I know their facilities, is superb, even competitive price, but I dont think they will offer you an individual solution. Other thing you should account for is the authority to take your checkride, btw wich is your license?
It just occured to me that FUMEC in Belo Horizonte wanted to accquire a 737NG SIM, not sure if it was supposed to be a "D" level. Fumec is a private university, wich offers aeronautical sciences course and they have an agreement with VRG (Gol).
Wouldnt hurt to check on that...
cheers