Just to add context to this 10M DEC-B figure for those reading

10MDEC-B=8M DEC or 50K Vouchers
50K Vouchers is obtained in 1200 days for staking 1M SPS (vouchers only), or 137 days including SPS + GLX rewards 600 or 69 days for 2M etc (at current drop rates, would be obtained faster through past rates)
1M Staked SPS voucher only reward would yield you 1 Plot survey per 29 Hours or per 3hours 20minutes for all rewards
8M DEC = $4950 (at 1k DEC = 0.61875, voucher cost is slightly less)
1K plots = $130,000 (This is based on last market price, which is highly illiquid)
Tax rate is around 3.8% (very subject to price movements)

You can simply times amount of plots owned by $4.95 to get USD amount (current prices, using DEC-B discount).