I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

The distributions and allocations on your K1 will dictate what is attributed to you. 

Homeowners, your tenants ARE RESPONSIBLE IF THEY VIOLATE SANITATION RULES, phone 311 to report them.Dont let nwo mafffia dictate otherwise.

If its not someone you know the lender will dictate the terms.

Of course you don't want to over pay for land, but site conditions and construction type will dictate costs....is there underpinning?

Depending on the property far more than the acquisition price may be required and that will also dictate the best loan product. 

Quote from @Michael Smythe: @Jerry NoguerasRecommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

The financing will then dictate which markets are and aren't within your budget.

.- They often get sold Class C or D properties while using Class A assumptions - then wonder why they are losing money.Here's some copy & paste info that you hopefully find helpful:-----------------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

It's mostly Class A properties, a few Class B.You may find the below copy & paste info useful in addressing your question:----------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?