What's the use to buy trasher as u only have 75 plats...

Buy a lvl 20 10 plat damage ring for ur archer and if u want, buy some vanities for the rest of ur platinum or save them.

Use daily blessing's to get urself exp elixir and just keep on playing games. Remember that u can join into campaign 2 lvls below recommended lvl (as an example alien oasis 1 recommended lvl is 35 but u can join there as lvl 33).

To help ur lvling I suggest u to join a guild and seek for friends to join u to runs. Besides PL is more fun as u have friends to play with .