You might part out the intel 320 ssd if it's got another old drive. Ram tends to be expensive for that machine. You could try parting that out and just sell the machine with 4GB. You could sell off one gpu as they're unlikely to add much to the price. The problem here is that regardless of its starting price, this is still an old computer. Newer cards outpace the ones in it. 16GB can be extremely cheap on newer machines even though ram is still expensive as hell in that one. I suggested parting some of it out as someone may be looking for cheap replacement parts for a machine of similar age. If they're looking for a powerful configuration today to use with current software configurations, this wouldn't be the way to do it. Even if it's a very capable system, trying to run the newest software on older hardware always leads to inevitable issues due to lack of support and poor tuning.
The first generation mac pro market basically tops out under $1000. Without this how would you budget for potential repairs on an older machine while maintaining the savings of purchasing a used system. I'd try for $700 for the base system, then part out the rest. This may sound unappealing, but your expectations are set way too high. If there was no advantage to a newer system, there would be no reason to sell this one.
