Alex:

There's lots of choices out there. I also don't know what ska (sounds sorta familiar) means. but you mentioned he plays rhythm guitar, but need more info such as, does he play acoustic electric?, or a solid body electric?, is he probably going to learn to play lead? There's a lot of different sounds from different amps, some amps are modeling amps, some amps are just straight amplifiers. Lots of youngsters use pedalboards..

I'm a fender man also, and I play every kind of music, and have many amps, the one I use is a 1964 Fender dual showman with reverb and vibrato. This is a head only and sits on a speaker Cabinet that I modified and currently has 2 heavy duty 15" woofers 2 8" mid range and a bass horn. I've never found anything better and no place it won't get the job done, and after all these years its still in perfect condition. It weights probably 175 lbs or close to it.

A good starter amp for a rocker is a fender princeton 65 watts with a 12" fender blue speaker. probably 285 bucks. a good amp for a acoustic electric player for folk church etc is a Fender acousonic comes in two sizes small is probably 350 bucks large probably around 650 bucks.

Versitile amp for all around use is Roland Jazz chorus probably get a used one from Ebay for about 300 dollars.

If it country, its gotta be tube, there's only one and thats Fender, I would pick a tube head and buy the speakers seperately and start him with 2 12" cab. The old Fenders are built like a tank and will not wear out, only need minor repairs sometimes, and a occasional tube. A good middle of the road choice is a mid 60's Bandmaster reverb, If it has to be all in one cabinet there's the Fender twin reverb, the #1 pick for the last 1/2 century and still probably tops, especially to older musicians who have worked with them.
You can buy used and if you look for a couple of things you can do okay on tube amps. look close for signs of tampering, missing parts and most important almost flawless in cosmetics, look in the back, no water marks, chassy Looks clean. turn in on and try it, if its quiet and has lots of volume and no scratchy sounds when knobs is turned its probably a good amp.
Buying a solid state(no tubes) is risky business, in used, wouldn't do it unless I knew the amp or person selling.....

Some of my veiws on this subject, not set in stone, but I've been using guitar amps since 1946, and have played thru most all of them. Hope you find something of use in my book.... ............pose