I purchased a sporterized Japanese Type 99 7.7x58 rifle for $150 at a recent gun show and that included a box of Norma ammo and a Lee Loader kit.
The Arisaka rifle is basically a mauser action and can be relatively accurate.
If you want a "modern sportster" most likely you will want a telescopic sight. If you have a military Arkisak you will need a bent or welded bolt that is turned down. Based on your question you will likely want to convert the rifle to a different caliber and that will entail either a new barrel or a re-bored barrel and reamed chamber. You will also need a new stock. All of this will run you probably at least $200 to $400.
If you want a "project" to learn gunsmithing techniques upon, I would suggest you go out an purchase a nice 8mm mauser. So much has been written about customizing those rifles and you will find more choices in stocks, telescopic sights, and folks who will help you turn down the bolt handle. Customizing a firearm that has a real following, will be much less expensive. Also you can go to many pawnshops and gun shows and find lots and lots of sporterized military rifles in various calibers.
If you want to "modernized" something that has significance to you from a family perspective, I suggest you learn how to reload and then shoot the rifle "as is." Arisaka's are pretty hard to find now a days, especially in great condition. They exist but you might want to consider not modifying it.
Graff & Sons has loaded Horndady ammo for the Arisaka at reasonable prices. Norma ammo is very expensive but also available.
Enjoy your rifle. I have been enjoying mine. I also have some "pure" military surplus rifles that are just as they left their military factory. It is fun to shoot a piece of history.