I've been slowly building up some solar panels but have held back on buying batteries, mainly because I'm fugal and want to find the best bang for my $$. Does anyone in the HTF have any sources for lithium or deep cycle batteries?

You looking to build your own battery system from cells or do you want a pre-packaged battery?

How much capacity are you looking for?

Im somewhat challenged when it comes building my own. But it isnt out of the question. But would prefer to buy a pre-packaged battery.
If building my own if significantly cheaper then I would consider learning how.
I have 500 watts worth of panels right now. (picked them up over the last year and have $150 in them)

My advice is to get a Kill-a-Watt device or something similar (measures KWhr used) and then check each device you want to power for at least 1 day in the conditions you expect to power them in, so you can find out how much energy you need for one day and then size your battery bank off of that.

To give an example, I checked my deep freezer in the garage during the Spring and it was using around .6 KWhr per day, but re-checked it during the summer (95 degree days) and the consumption was at 2KWhr per day or about 3 times what I had started planning on.

Once you have all your loads figured out, then you need to figure out the time you want to power them and that may be days as the sun may not shine each day.  Then size your battery bank off of that.

For example, if I wanted to power my deep freezer during the worst conditions, I would need around 2KWhr per day and if I wanted to power it for say 5 days, then I would need a 10KWhr battery bank at full discharge, so I would probably add in around 25% extra, so I didn't draw the bank down to zero, so it would end up being around a 12.5KWhr battery bank.

Couple more items popped into my head.

Do you have an all-in-one inverter already, so that you can charge the battery bank with the solar panels and then use the battery bank to power other items?

You might also look at a pre-made system (I have a Bluetti AC200P that I'm pretty happy with) and then pair your solar panels with it (if you can will depend on the specs on the solar panels).  I know a bunch of companies are releasing new products this fall that look very nice.

Here is a forum if you want to get into the DIY aspect (https://diysolarforum.com/) along with a web-site (https://www.mobile-solarpower.com/) and YouTube channel (https://www.youtube.com/c/WillProwse/videos.)