+1 on pretty much all of madhatte's comments above (tried to rep you, but . . . )
I normally do not think of the Silvey grinders due to the price, and have never used one. But they do have a good reputation if you do a large number of chains, and can afford one, or can find a good deal on a used one in good condition.
I do not advise anyone to buy the $30 plastic grinders which I consider to be junk and a waste of money. I discourage people from buying the $100 Chinese knock off grinders, due to the uneven quality and the uncertain long term life and value. Plan to spend a bit of time to tune one of these up, with the possibility that you cannot (e.g. bent shaft, bad bearings, etc.), and plan to replace the wheels up front.
The Oregon grinders are the standard that others are compared to. They are made in Italy by Tecomec and also sold under the SpeedSharp and other names. You may find a good deal on them under the other names. Repair and replacement parts are readily available. They keep their value if you decide to sell it or upgrade later. They are the minimum that you should consider for the volume of chains you mention.
A bench mounted grinder lets you sharpen a batch of chains at one time. I have mine mounted on a thick board that I can clamp to any surface. I can set it up in my shop. I have clamped it outside to a picnic table on nice days to keep the noise and dust out of the house. I have run one in the field off of a generator.
The bar mount grinders have smaller, less powerful motors. They use smaller diameter wheels, which heat up the cutters more. They require you to mount each chain on the saw (hard to do batches of chains) unless you set it up on a spare bar in your vise. The only real advantages of bar mount grinders is when sharpening a hard-to-change chain, such as on a chainsaw mill, or if you get a 12v model that you want to run off of your truck battery in the field. I would consider one only as a secondary grinder for the volume you describe.
The Maxx grinder advertises a reversible motor, which seems like an important advantage, but in practice, millions of guys cut with chains ground on single directional grinders. The Maxx grinders also have received less favorable reviews from guys on A.S. that I respect.
Bottom line: Oregon 511ax, SpeedSharp, Tecomec Super Jolly, or equivalent ($300-$400). Silvey if you can afford one or get a good deal on a used one.
Philbert