What would be a good bike which would be low priced and work for a rookie?
Forget about chain store big box stuff - cheap, nasty and comes with no support, They typically ride like pigs, and are usually exceptional heavy. You get exactly what you pay for - I won't put by 10 year old on one.
Cheapest is second hand, next cheapest is last years model on 50% mark down. Either way, go visit the LBS's around you and find one that has lots of kids bikes - its a sign they know about tight budgets. They also tend to be keen on the returning customers (kids grow out of bikes really quickly), so tend to give good service despite you not putting downs $1000's on a flash bike.
Do not pay sticker price. negotiate.... You will also need things like pump, helmet, spare tube etc. The LBS will also make sure you get the right sized bike.
If they are still out of your price, ask if they will check a second hand bike if you bring one in. A few dollars spent doing this and you will end up with a better bike for less money than a chain store bike.
This is highly dependent on the market you're in. The most important thing to do is have a bike that fits appropriately. You may want to look at used mountain bikes as well, since you usually get more bang for your buck there (but get the frame and wheels and stuff checked over before you buy, so there are no cracks and unwelcome surprises).
I would recommend sticking with a hard tail to begin with (front fork, rear rigid). Wheel size is personal - 26" or 29" are recommended since they are cheaper than 650b, with 26" probably being a bit cheaper than 29", but this is still preference. Decent disc brakes are a plus (probably hydraulic ones are favorable, but you'll survive with mechanical) but remember for many years people used V brakes or canti's and were alright. There are a variety of budget forks out which are suitable for beginners to go offroad made by companies like SR Suntour primarily (their XC_ lines), and a bit fancier ones made by RockShox, Marzocchi, Fox, etc - a lock out feature is useful if you're also using it on the road. Tire selection is surface dependent. Since its your first bike, you can be a bit cheap with components like derailleur, shifters, etc. (Acera level should be fine), and upgrade things as they break.