I've had a chance to actually look at all the Essentials products now, so I can give a better answer rather than just a guess, so I've edited accordingly.
Thanks to DDI going online only, it's no longer possible to subscribe for 1 month and download all the prior content for $10. That'd really keep things in around $10 for everything. As is you'd need to buy HeroLab with the Authoring Kit for $30, and pay another $10 on top for one month of DDI to get all the content. That puts you at $40.
If we're looking at Amazon prices it's a lot better, since you're talking $14 for the core books. You need just one of the Heroes books. Rules Compendium is nice to have, but isn't necessary as the important stuff is covered in the DM's Kit. The reverse is also true, although I consider the extra content in the DM's Kit (screen, tokens) to be of more value than the extra rules you probably won't use in the Compendium.
So you could look at $14 as a player for Heroes of the Fallen Lands or Heroes of the Forgotten Kingdoms. As a DM you'd want Monster Vault and DM's Kit, which would come in at $46. If you want to go really cheap, Monster Vault and Rules Compendium would cost you $34, which is viable if you already have a lot of experience DMing and are just looking for affordable rules at the table.
It's also worth noting that the D&D Adventure Game Red Box, while completely unnecessary, is a great tool for complete newbies to the game to make a character without being overwhelmed. For them, having Heroes of the Fallen Lands would be much more useful than Heroes of the Forgotten Kingdoms.
The original 3 core books are also going for less than half price on the used market now, which could run you $30, without having to pay tax. That's of course YMMV, but you won't see anything like that for Essentials (yet).