Research in Motion (RIM) has nearly 800,000 BlackBerry PlayBook tablets sitting idle in inventory. RIM had $1.372 billion in inventory at the end of last quarter, up from $618 million at the end of February, according to findings from the Guardian.

RIM’s PlayBook was manufactured by Quanta Computer at their Taiwan factory. Fubon Securities analyst Arthur Liao said that the company had shipped 1.5 million PlayBooks in the first half. Production has declined significantly as of late as RIM struggles with excess inventory.

Last week RIM announced they had only shipped 200,000 tablets in the second quarter. Earlier accounts from the company say they shipped 500,000 PlayBooks in the first quarter. Simple math tells us that if they did receive 1.5 million units from Quanta, there are some 800,000 PlayBooks still unaccounted for.

Earlier this month we reported that Best Buy had slashed $150 off the 64GB tablet and $50 off the 16GB model, bringing the prices down to $550 and $450 respectively. It’s a good start but RIM will have to do much better to keep the remaining 800,000 tablets from collecting more dust.

Perhaps RIM should take a page from HP’s playbook (no pun intended) and drop prices to $99 for the entry-level PlayBook to clear out excess inventory. At the current rate and price point that RIM has on the tablet, it’s unlikely that they will push 800,000 units anytime soon.

The Guardian notes that RIM indicated in their earnings call last week that they would start price promotions over the second half of the year to get devices in customer's hands.