Essentials had a somewhat significant price drop earlier this year (around February/March) which resulted in an increase in the cost of the upgrade.
So there are multiple upgrade options for Essentials, depending on when you purchased it, whether or not you bought it stand-alone, or if you bought it with Balance and already owned a previous version of reason or record.
If memory serves, there is a drop down menu to select what product you are upgrading from.
Perhaps contact Props support with your Essentials purchase information and ask them to walk you through buying the upgrade to full Reason 6.5.
HP Pavillion DV7T-3300 Laptop | i7 Q720 @ 1.6 GHz | 4GB RAM | Win7 Pro 64-bit
m-audio Axiom Pro 61 keyboard controller || iPad2 | RetouchControl DUO | TouchOSC | LoopBe30 MIDI
m-audio Mobile Pre USB (original) audio interface | ASIO4ALL || RØDE NT-3 mic
Reason 6.5.3 || Pulsar | Saturation Knob | Rough Rider | TSAR-1 | Uhbik-A | Re-Tron | Polar | Echobode | Uhbik Q | Uhbik F | Morfin XF | Uhbik S | Uhbik D | Uhbik G | CV Suite Line Processor | wbl5515 | Uhbik P | RE-2A | Radical Piano