I would really recommend you to invest in an X13 ASIC (ie Baikal miner) or rent power using NiceHash or miningrigrentals.com. GPU mining will not get you very far by this point. You could also mine one of the profitable coins from the link below, and then buy ONION with the profit, it will get you more ONIONs

https://whattomine.com/coins?utf8=✓&adapt_q_280x=0&adapt_q_380=0&adapt_q_fury=0&adapt_q_470=0&adapt_q_480=0&adapt_q_750Ti=0&adapt_q_10606=0&adapt_q_1070=1&adapt_1070=true&adapt_q_1080=0&adapt_q_1080Ti=0ð=true&factor%5Beth_hr%5D=30.0&factor%5Beth_p%5D=120.0&grof=true&factor%5Bgro_hr%5D=35.5&factor%5Bgro_p%5D=130.0&x11gf=true&factor%5Bx11g_hr%5D=11.5&factor%5Bx11g_p%5D=120.0&cn=true&factor%5Bcn_hr%5D=500.0&factor%5Bcn_p%5D=100.0&eq=true&factor%5Beq_hr%5D=430.0&factor%5Beq_p%5D=120.0&lre=true&factor%5Blrev2_hr%5D=35500.0&factor%5Blrev2_p%5D=130.0&ns=true&factor%5Bns_hr%5D=1050.0&factor%5Bns_p%5D=155.0&lbry=true&factor%5Blbry_hr%5D=270.0&factor%5Blbry_p%5D=120.0&bk2bf=true&factor%5Bbk2b_hr%5D=1600.0&factor%5Bbk2b_p%5D=120.0&bk14=true&factor%5Bbk14_hr%5D=2500.0&factor%5Bbk14_p%5D=125.0&pas=true&factor%5Bpas_hr%5D=940.0&factor%5Bpas_p%5D=120.0&factor%5Bskh_hr%5D=26.5&factor%5Bskh_p%5D=120.0&factor%5Bl2z_hr%5D=420.0&factor%5Bl2z_p%5D=300.0&factor%5Bcost%5D=0.1&sort=Profit&volume=0&revenue=current&factor%5Bexchanges%5D%5B%5D=&factor%5Bexchanges%5D%5B%5D=bittrex&factor%5Bexchanges%5D%5B%5D=bleutrade&factor%5Bexchanges%5D%5B%5D=btc_e&factor%5Bexchanges%5D%5B%5D=bter&factor%5Bexchanges%5D%5B%5D=c_cex&factor%5Bexchanges%5D%5B%5D=cryptopia&factor%5Bexchanges%5D%5B%5D=poloniex&factor%5Bexchanges%5D%5B%5D=yobit&dataset=Main&commit=Calculate