Crack in left front portion of sway bar. Is it possible to weld? The crack is on the back side of the bar saw it when doing brakes and rotors. How much should I spend on a new/used sway bar if welding is not an option. It appears to be about 1/8" crack and 1-1/12" long.

My suggestion would be to completely weld up the hole and re-machine the hole and threads and make sure you are using a grade-8 bolt when putting it back together. Possibly go up one size in the bolt if possible.

Are you sure it is the sway bar you are looking at? Sway bars are bent to start with to do their jobs so the left end will be a mirror to the right end. So by 'bent' I'm assuming you mean one side isn't a mirror to the other.
Most sway bars are mounted with 6 bolts. 1 bolt at each end at each hub and two on each U clamp holding the sway bar bushes in place. Sway bars need to flex and bend to do their job so they shouldn't be welded in place.
Could you comment below with photos of the part your looking at and where it is on the vehicle?
On some vehicles you'll need to lower the front sub frame to get the actual sway bar out so it's often a job you can't really do on you drive.
Comment below with more information and I'll try to help you more.

You didn't mention year make or model. If this is for a Dodge caravan the following instructions apply. You will need a floor jack, jack stand, bungee cord, 3/8" & 1/2" torque wrench, mallet, 6" 1/2" extension, set of 3/8" and 1/2" metric wrenches and shallow sockets, 3/8 torx bit sockets, large pair of vice grips, 3" or 4" electric cut off saw and penetrating oil. NOTE: Use the penetrating oil on all nuts and bolts before they are removed. The vice grips and cut off saw is to help remove the anti sway bar link if the nut seizes or strips. You may not be able to reuse the existing anti sway bar link. Loosen the lug nuts, raise the wheel off the ground, place the jack stand underneath the subframe or pinch weld where the emergency roadside jack would go, remove the wheel, remove the lower anti sway bar nut, position the bungee cord from the subframe to the brake rotor (This will support the brake assembly so you don't over extent the CV joint), remove the wheel speed sensor cord (if applicable) from the strut mounting bracket, remove both large bolts from the lower strut mount, remove the three nuts from the upper strut mount (support the strut before you remove the last nut) and lastly remove the upper anti sway bar nut. Reassemble in the opposite order. Torque specs- (3) Top mount nuts: 21-25 ft lbs. (2) Anti sway bar link nuts: 65 ft lbs. (2) Lower strut mount nuts and bolts: 65 ft. lbs. Plus 1/4" (90 deg.) Additional Turn and (5) wheel lug nuts: 100 ft lbs. Any questions please feel free to write back.

Could be a bad tire ( or bent rim Have balance checked), ball joint, idler arm, wheel bearing, steering tie rod end or defective rack and pinion unit. Lift vehicle about 1 inch off ground ( do each side independently) Use a pry bar and pry from ground up and down on wheel. Much play? bad ball joint. With both hands, try to move wheel side to side. Much play? could be a tie rod end or bad wheel bearing. Visually check play of steering arm into rack and pinion unit, more than about a half inch play, bad rack and pinion unit. Try to move back and forth with hands top and bottom. Much play? Bad ball joint or wheel bearing, verify visually that it is ball joint moving, else it is the wheel bearing. Manually check for play in each joint in steering control rods from steering knuckle all the way through each rod where there is a joint. Replace the one you find excessive play in. Check mounting studs for sway bar for loose fit, deteriorated rubber bushings or a crack / break in the sway bar. Replace if needed. That's about all I can think of unless it only happens when applying brakes, in which case it could be a warped rotor.

may have a callipper sticking on front

There are so many possibilities. It's difficult to even attempt a guess.but... Axles, ball joints, brake calipers, rotors, sway bar ends/bushings, rack and pinion,tie rod ends, A-arms, shocks, struts, springs, mounts and even a cracked or broken frame! Hope this was helpful!

Is it a broken weld or break near a weld

I would fabricate a new part & weld it on,
or do something with whatever the issue is

sounds like you may have a cracked Rack N Pinion, could be that something needs to get Welded down there. Something like the Rack Pinion casing can crack and allow the CV shaft to protrude far enough to hit your ball joint during turns thus hindering rotational movement

you will need to disconnect the sway bar from the sway bar links(in most cases you might as well replace the links as well since they may snap while trying to remove them). You will then remove the sway bar bushing caps 2 bolts on each of the 2 caps and lower the sway bar. Is the bar cracked? should not require replacing if it isn't cracked. the rubber bushings and links do wear over time and yes the bar can crack.

My dear if according to you,

You've replaced tie rod ends, lower ball joints, sway bar links, struts and strut ends, and the warped brake rotors and the issue is still at hand; then you ought to consider replacing the hubs.

Good luck.