This really depends on what you need, I integrated our sql based previous site, with 10K lines and 60 K customers. Many inventory apps mucked up our database so I removed them and made lots of things simple.
Also depend on if you ship or do you have stock locations etc.
We only have the 79 euro shopify package which is enough for us.
I built in orderly print to follow our backorders, (free then there is a smaller fee)
Auto purchase orders to order from suppliers, (free then there is a smaller fee)
Our main stock is kept in shopify and feeds to quickbooks, quickbooks is 36£
Dpd app, which is free, or there is a small fee, but after a while if you ship more you will need to pay a little more. For us it was not beneficial yet to pay a lot for shipping providers, as we have extremely great fees from couriers. We also connected Royal Mail, so with few clicks we can create labels.
We also moved away from Mailchimp and using the shopify email for marketing saving few hundreds on this each month.
We firstly used shopify payments, but they are painfully slow! Then we are now using sagely and elavon so we get all card payments next morning by 9am. However ! this is really expensive as Shopify chucks another 1% card fee, so we are not very happy about this.
I really struggled getting help from the forum when tried to build in apps, nobody was helpful and spent endless nights to find the best option.
For inventory you have to pay a lot and you have to be careful as many app owners have no clue and they can ruin your data!
We pay in total for these 500£ roundly each months, we have 100 order per day roughly and ship worldwide with 200 K stock and 1M turnover.
Good luck, you can save money on lots of apps and have a great store.