hello, we are an exporter of hardwood (ipe) located in South America. It is pretty common for importers to buy nice and expensive decking and then put something inferior underneath. Maybe the theory behind this is that you do not see the framework anyway, anyhow, the frame is the building basis of it all and if this starts to rot first then your entire deck needs to be dismantled. I would therefore recommend some hardwood and it is not so important which kind. Please do remind that cumaru is very hard, but it does not mean that it is very resistant to decay, in fact cumaru - despite being very hard - is prone to decay and rots in humid conditions (underneath your porch is such place. I would recommend for your framework your garapa, or ipe, itauba or angelim vermelho, curupau, iroko or azobe. These are THE species against rot.
Against end cracking of the boards you need to wax the ends, we do this here with paraffin (USD2/kg), I don't know what is available in your town. For much more information on installation please see the link given below:

Here is a link that might be useful: manual on building your own deck

Thank you for your time and input.

It turns out Advantage likes to leave old sales posted on their site when they actually have nothing in stock at those good prices. I'm waiting to hear back from East Teak to see if we can use hardwood at all.

baby: All the pros on this site will say using PT framing is fine. Roquevalente is getting a bit too commercial for this site's self-promotion policies. It's pressure treated to last a long time, and it's perfectly suitable for framing. The decking is what takes a beating, and is worth spending more money on.

Keep watching the pricing on the various web sites. Or you might try calling some of them to see if they've got some sort of odd lot sizes or something that you can get at a discount.

As for sealing, you'll get opinions on both sides here. We put anchor seal on the ends of each board. Some say it's a crock. Your decision. :-)