In my opinion it's preferable to wager 500,000 satoshis to receive 1 GT than purchasing each of them for 25,000 satoshis, though.
The point it that if you do "reasonable" decisions, you will end with more than 475k sat if you wager 500k. Which means that you not only received 1GT (additional benefit), but also you have a "base" profit. You just need to decide what to do with 500k sat, while many "small" players do not bet so much - anyway I think it is quite easy doable in a few months.
It also depends a lot on the amount of luck you have so it is possible to end up with a total of a lot lower than 475 k also. I know you also get a lot of RP if you would wager so much but don't forget that the house edge is also 5%.