Hmm, I don't know about that though. Even 5th (or last) place in the wagering contests of some of the less popular coins is pretty much unattainable for regular players.
Some examples ~
I don't think combined, total monthly wagers are a good measurement to say whether or not competing in a contest is affordable.
Especially with low house edges like CG has them, you can wager a lot of money even with a small or medium starting balance (-> deposit).
Thus I would look at the -EV those players on the places you pointed out currently have. I'll use Dice (0.8% HE) for my calculation, as it gives us the lowest number and as Dice is the most popular game.
The numbers I'll get is what the players are expected to have lost when wagering what they have wagered, for the question on whether or not something is "affordable", I think that's a good number/measurement.
5th place for Stratis: 10,447 STRAT = 15879 USD * 0.008 = $127.04
5th place for Peercoin: 2,859 PPC = 3202 USD * 0.008 = $25.62
5th place for Ethereum Classic: 872 ETC = 10812 USD * 0.008 = $86.49
5th place for NEOGas: 243 GAS = 1372 USD * 0.008 = $10.98
5th place for Dash: 9.04 DASH = 1292 USD * 0.008 = $10.34
7th place for Dogecoin: 5,509,476 DOGE = 13184 USD * 0.008 = $105.47
5th place for Monero: 12.75 XMR = 1199 USD * 0.008 = $9.59
7th place for Litecoin: 205.08 LTC = 11638 USD * 0.008 = $91.10
As you can see, you can realistically reach those wager numbers even with some small/medium deposits.
If you're just gambling a couple of hundred USD worth of crypto every month or so, you'll never get any prize. I'd call someone like that a small regular player.
If you can afford to risk and possibly lose between $10 and $150 worth of crypto a month, you have a realistic chance of scoring a prize on the wagering contests.
I wouldn't say the wagering contests are exclusive to high rollers, with that in mind.