A little outside your price point of $150 the Shapton Pro Kit comes in at $177http://www.chefknivestogo.com/shpro3pcset.html
Or if you wanted some kind of holder and flattener $175http://www.chefknivestogo.com/sh6pcstset.html
Kind of gonna go off off book (just to get you at your price point) with this for $160:
$50 Holder and Flattening Plate http://www.chefknivestogo.com/xxcdiplandun.html
$60 Nubatama Bamboo Combo Stone 150/1200 http://www.chefknivestogo.com/nubacost15.html
$50 Suehiro Rika 5000 Grit Stone http://www.chefknivestogo.com/suri50grst.html
My primary recommendation is the Shapton Pro especially if you are a starting freehand for first time. Stones cut fast, are hard and splash and go. A lot of the long soak stones are soft and easily gouged especially at high grits or wear down faster. Or if they are hard price out of your budget.
Ok I had 1 more thought and probably what I would do if I had $150...............>
-Just get a Shapton Pro 1000 grit at $52, the universal stone holder with 140 grit generic diamond plate for $50. And 8" Felt Strop for $12/15 plus diamond paste for $12. Total $127/130.
The beater/practice knives you can use the generic diamond plate to set bevel then go to the Shapton 1k then finish on the loaded strop. Will it be the most refined edge, no but it will be completely serviceable. Your new knives you can just use the Shatpon and loaded strop and call it a day.
Then your next purchase can be a Shapton 5K to get you that more refined mirror edge. The generic will still be good for practice/beater knives. And your purchase after that can be low grit Shapton 220. Then you could always purchase the Atoma 140 grit to replace the generic plate after the Shapton 220. That way you have your next 3 or 4 purchases already lined up And if it takes 12-18 months even 24 months for Atoma no big deal.