The default and random acoins offers are no longer common with good prices. Most of them are fraudulent prices. You can trigger the best offer by level 7 upgrade of certain equipment and Mech per rank. The higher star it is the greater amount of acoins offer you trigger to purchase. Example:
2 stars level 7 brings 100-400 acoins = 1-3 bucks 3 stars level 7 brings 600-800 acoins = 3-5 bucks 4 stars level 7 brings 1200-1500 acoins = 9-12 bucks 5 stars level 7 brings 1800-2300 acoins = 15-20 bucks 6 stars level 7 brings 2500-3500 acoins = 25-30 bucks
It is advisable to keep the rest of unimportant equipment or Mechs for future upgrade to trigger Acoins offer to use those cheap Acoins offers for the upgrade of your main Mechs.
Note: the price tables are not absolute, they may be inaccurate or refer to average prices near the estimation of original prices.