Reloading wil be cheaper than buying factory ammo in the looooooong run. If you want consistant, accurate, LR worthy loads, then you DO need to handload. if you start handloading for precision LR shooting then you need precision handloading equipment. Dont get the basic RCBS FL sizer and seater. There are a number of good dies available and some I would recommend considering would be Redding bushing dies, either the FL die or the neck sizer and body die and definitely the competition seater. If you go with bushing dies, then you need to turn your necks. The standard neck sizing die can be used effectively also if you set it up right. Above all, get a competiton seater. Your dies and your technique for using them are probably your most important ingredient in precision handloading. I wouldn't buy any books on handloading. There is more than enough knowledge and experience in these forums to get you going.
Your costs with handloading will include your equipment, which if you're doing this right, will cost well in excess of $500. You can get a lot of stuff on ebay for a good price or even in the classifieds here. You will also have load development costs that you dont have with factory ammo. You can easily go through 100 rounds or more looking for and fine tuning your load.
If you want to shoot a 300 mag, then I would recommend the WSM. There are a lot of guys who like their 300 WM and it's a good cartridge, but the WSM is basically the ballistic twin of the WM and will have double or more the barrel life.
I think the Senedero is a great choice and I have one in 300 RUM and 25-06. If you're going to buy one off the shelf then the WSM is not an optuion. If your goping to use one to build, then I say do the WSM. I like the older SF's vs the newere SFII's. The SFII's have a wider beaver tail forearm and palm swell. If you like that, then go with the SFII. I'm not a big guy like you, 5'7" and 160 and 53, and I have no problem carrying my Sendero around. I just got back from antelope hunting
where I carried my Sendero with 2 lb NF scope 10 miles on foot this past Sunday. Ended up shooting my buck 200 yards off the road, lol.
Welcome to LRH and good shooting,
P.S. If you put the calc to it, shooting 1000 rounds @ $3 per round will cost you $3000. You can buy the best handloading equipment and over 2000 rounds of worth of componants at $1 per handloaded round. If you do much shooting, it wont take you long to "save" up for some custom gun work. Just remember... buying stuff on sale isn't spending, it's saving